Document and Entity Information Document Information [Table] Class of Stock [Axis] Class of Stock [Domain] Common Stock [Member] Ordinary Shares ADR [Member] American Depositary Shares Represents information pertaining to non-voting ordinary shares. Non voting ordinary shares Non-voting ordinary shares Document Information [Line Items] Document Information Document Type Document Annual Report Document Period End Date Document Transition Report Securities Act File Number Entity Registrant Name Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Address, Address Line One Entity Address, City or Town Entity Address, Country Entity Address, Postal Zip Code City Area Code Local Phone Number Title of 12(b) Security No Trading Symbol Flag No Trading Symbol Flag Trading Symbol Security Exchange Name Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Current Reporting Status Entity Interactive Data Current Entity Filer Category Entity Small Business Entity Emerging Growth Company ICFR Auditor Attestation Flag Document Financial Statement Error Correction [Flag] Entity Shell Company Entity Public Float Entity Common Stock, Shares Outstanding Entity Central Index Key Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Period Focus Amendment Flag Auditor Name Auditor Location Auditor Firm ID Consolidated Balance Sheets Statement [Table] Statement [Line Items] Statement Assets [Abstract] Assets Assets, Current [Abstract] Current assets: Cash and Cash Equivalent Cash and cash equivalents Prepaid Expense and Other Assets, Current Prepaid expenses and other current assets Amount of research and development incentives receivables, classified as current. Research and Development Incentives Receivable, Current Research and development incentives receivable Assets, Current Total current assets Property, Plant and Equipment, Net Property and equipment, net Operating Lease, Right-of-Use Asset Operating lease right-of-use assets Other Assets, Noncurrent Other assets Assets Total assets Liabilities and Equity [Abstract] Liabilities and shareholders' equity Liabilities, Current [Abstract] Current liabilities: Accounts Payable, Current Accounts payable Accrued Liabilities, Current Accrued expenses and other current liabilities Accrued expenses and other current liabilities Deferred Revenue, Current Deferred revenue, current portion Liabilities, Current Total current liabilities Operating Lease, Liability, Noncurrent Long term lease liabilities Operating lease liabilities, net of current portion Deferred Revenue, Noncurrent Deferred revenue, net of current portion Other Liabilities, Noncurrent Other longterm liabilities Liabilities Total liabilities Commitments and Contingencies. Commitments and contingencies (Note 11) Equity, Attributable to Parent [Abstract] Shareholders' equity: Common Stock, Value, Issued Ordinary shares, including non-voting ordinary shares, £0.01 nominal value; 159,685,229 and 155,876,645 shares authorized at December 31, 2025 and December 31, 2024, respectively; 69,367,896 and 69,061,418 shares issued and outstanding at December 31, 2025 and December 31, 2024, respectively Additional Paid in Capital Additional paid-in capital Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive (loss) income Retained Earnings (Accumulated Deficit) Accumulated deficit Equity, Attributable to Parent Ending balance Beginning balance Total shareholders' equity Liabilities and Equity Total liabilities and shareholders' equity Common Stock, Par or Stated Value Per Share Ordinary shares, nominal value Common Stock, Shares Authorized Ordinary shares, shares authorized Common Stock, Shares, Issued Ordinary shares, shares issued Common Stock, Shares, Outstanding Ending balance (in shares) Beginning balance (in shares) Ordinary shares, shares outstanding Consolidated Statements of Operations and Comprehensive Loss Revenue from Contract with Customer, Excluding Assessed Tax Collaboration revenue Revenue from collaborative arrangement Operating Expenses [Abstract] Operating expenses: Significant segment expenses: Research and Development Expense Research and development Total research and development General and Administrative Expense General and administrative Total general and administrative Operating Expenses Total operating expenses Operating Income (Loss) Loss from operations Nonoperating Income (Expense) [Abstract] Other income (expense): Interest and Other Income Interest and other income Interest Expense, Nonoperating Interest expense Gain (Loss) on Extinguishment of Debt Loss on extinguishment of debt Loss on extinguishment of debt Difference between the amount paid to settle and carrying amount of research and development funding liability which is extinguished. Gain (Loss) on Extinguishment of Research and Development Funding Liability Gain on extinguishment of research and development funding liability Gain on extinguishment of research and development funding liability Nonoperating Income (Expense) Total other income, net Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Net loss before income tax provision Income Tax Expense (Benefit) Total provision for (benefit from) income taxes Provision for (benefit from) income taxes Net loss Net loss Earnings Per Share, Basic Net loss per share, basic (in dollars per share) Earnings Per Share, Diluted Net loss per share, diluted (in dollars per share) Weighted Average Number of Shares Outstanding, Basic Weighted average ordinary shares outstanding, basic (in shares) Weighted Average Number of Shares Outstanding, Diluted Weighted average ordinary shares outstanding, diluted (in shares) Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Comprehensive loss: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Other comprehensive income (loss): Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Foreign currency translation adjustment Comprehensive Income (Loss), Net of Tax, Attributable to Parent Total comprehensive loss Consolidated Statements of Shareholders' Equity Equity Components [Axis] Equity Component [Domain] Additional Paid-in Capital [Member] Additional Paidin Capital AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) Retained Earnings [Member] Accumulated Deficit Sale of Stock [Axis] Sale of Stock [Domain] Represents information pertaining to Ionis Share Purchase Agreement. Ionis Share Purchase Agreement Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (decrease) in shareholders' equity (deficit) Stock Issued During Period, Value, Stock Options Exercised Issuance of ADSs upon exercise of share options Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Exercised Issuance of ADSs upon exercise of share options (in shares) Stock Issued During Period, Value, New Issues Issuance of ADSs and non-voting ordinary shares, net of commissions and offering expenses Aggregate purchase price Stock Issued During Period, Shares, New Issues Issuance of ADSs and non-voting ordinary shares, net of commissions and offering expenses (in shares) Shares issued (in shares) Stock Issued During Period, Value, Restricted Stock Award, Gross Issuance of ADSs upon settlement of restricted share units Stock Issued During Period, Shares, Restricted Stock Award, Gross Issuance of ADSs upon settlement of restricted share units (in shares) APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Share-based compensation expense Payments of Stock Issuance Costs Commissions and offering expenses Consolidated Statements of Cash Flows Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Cash flows from operating activities: Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Adjustments to reconcile net loss to net cash used in operating activities: Share-Based Payment Arrangement, Noncash Expense Share-based compensation expense Depreciation, Depletion and Amortization Depreciation and amortization Amount of the cost of borrowed funds accounted for as non cash interest expense. Non Cash Interest Expense Non-cash interest Deferred Income Tax Expense (Benefit) Deferred income tax (benefit) provision Total deferred income tax (benefit) provision Other Noncash Expense Other non-cash charges Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Increase (Decrease) in Accounts Receivable Accounts receivable The increase (decrease) during the reporting period in amount due within one year (or one business cycle) for research and development incentives receivable. Increase (Decrease) in Research and Development Incentives Receivable Research and development incentives receivable Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses and other assets The increase (decrease) during the period in the carrying value of operating lease right-of-use assets reported as assets that are due to be disposed of within one year (or the normal operating cycle, if longer). Increase (Decrease) in Operating Lease Right-of-use Assets Operating lease rightofuse assets Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Accrued expenses and other current liabilities Increase (Decrease) in Operating Lease Liability Operating lease liabilities Increase (Decrease) in Deferred Revenue Deferred revenue Increase (Decrease) in Other Noncurrent Liabilities Other long-term liabilities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Net cash used in operating activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Cash used in investing activities: Payments to Acquire Property, Plant, and Equipment Purchases of property and equipment Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Net cash used in investing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Cash flows from financing activities: Repayments of Long-Term Debt Repayment of debt Total aggregate payment Proceeds from Issuance of Common Stock Proceeds from the issuance of ADSs and non-voting ordinary shares, net of issuance costs Proceeds from Stock Options Exercised Proceeds from the exercise of share options and settlement of restricted share units Finance Lease, Principal Payments Principal payments on finance lease obligations Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Net cash (used in) provided by financing activities Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Effect of exchange rate changes on cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Net increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Cash, cash equivalents and restricted cash at end of period Cash, cash equivalents and restricted cash at beginning of period Total cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation [Abstract] Reconciliation of cash, cash equivalents and restricted cash Restricted Cash and Cash Equivalent Restricted cash included in prepaid expenses and other current assets Restricted Cash and Cash Equivalent, Statement of Financial Position [Extensible Enumeration] Restricted Cash Equivalent, Current Restricted cash included in prepaid expenses and other current assets Restricted Cash and Cash Equivalent, Noncurrent Restricted cash included in other assets Supplemental Cash Flow Elements [Abstract] Supplemental disclosure of cash flow information Interest Paid, Excluding Capitalized Interest, Operating Activity Cash paid for interest on debt Finance Lease, Interest Payment on Liability Cash paid for interest on finance lease obligations Income Taxes Paid, Net Cash (received from) paid for income taxes Total Operating Lease, Payments Cash paid for amounts included in the measurement of operating lease liabilities Increase or decrease in future cash outflow to pay for purchases of fixed assets that have occurred. Increase Decrease Capital Expenditures Incurred but Not yet Paid Changes in purchases of property and equipment in accounts payable and accrued expenses Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Non-cash impact to operating lease right-of-use assets and operating lease liabilities Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Property and equipment obtained under finance leases Nature of the business and basis of presentation Business Description and Basis of Presentation [Text Block] Nature of the business and basis of presentation Summary of significant accounting policies Significant Accounting Policies [Text Block] Summary of significant accounting policies Fair value of financial assets and liabilities Fair Value Disclosures [Text Block] Fair value of financial assets and liabilities Property and equipment, net Property, Plant and Equipment Disclosure [Text Block] Property and equipment, net No definition available. Accrued expenses and other current liabilities The entire disclosure for accrued expenses and other liabilities that are classified as current at the end of the reporting period. Accrued Liabilities and Other Liabilities Disclosure, Current [Text Block] Accrued expenses and other current liabilities Debt Debt Disclosure [Text Block] Debt Ordinary shares Equity [Text Block] Ordinary shares Share-based compensation Share-Based Payment Arrangement [Text Block] Share-based compensation Significant agreements Revenue from Contract with Customer [Text Block] Significant agreements Income taxes Income Tax Disclosure [Text Block] Income taxes Commitments and contingencies Commitments and Contingencies Disclosure [Text Block] Commitments and contingencies Net loss per share Earnings Per Share [Text Block] Net loss per share Benefit plans Retirement Benefits [Text Block] Benefit plans Related party transactions Related Party Transactions Disclosure [Text Block] Related party transactions Segments and geographic information