v3.26.1
Impairment losses - Key assumptions used in value in use calculations (Details) - EUR (€)
€ in Millions
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2024
Impairment losses      
Key assumptions cash flow forecast period for licence and spectrum payments initial period for renewals and newly available spectrum 5 years    
Key assumptions period for management plan used in long term growth rate. 5 years    
Key assumption period management used forward looking equity market risk premium 10 years    
EBITDaL CAGR cash flow projection period 5 years 5 years 5 years
Capital expenditure cash flow projection period 5 years 5 years 5 years
Germany      
Assumptions used in value in use calculation      
Pre-tax risk adjusted discount rate 7.50% 7.80% 8.30%
Long-term growth rate 1.20% 1.20% 1.00%
Projected adjusted EBITDAaL (as a percent) 1.90% 1.30% 2.40%
Germany | Pre-tax discount rate      
Impairment losses      
Change in assumption that would lead to impairment 0.1   0.5
Germany | Long-term growth rate      
Impairment losses      
Change in assumption that would lead to impairment 0   (0.4)
Germany | Projected adjusted EBITDAaL CAGR      
Impairment losses      
Change in assumption that would lead to impairment (0.2)   (1.2)
Germany | Projected capital expenditure      
Impairment losses      
Change in assumption that would lead to impairment 0.5   3.9
UK      
Assumptions used in value in use calculation      
Pre-tax risk adjusted discount rate 9.10%    
Long-term growth rate 2.00%    
Projected adjusted EBITDAaL (as a percent) 7.70%    
UK | Pre-tax discount rate      
Impairment losses      
Change in assumption that would lead to impairment 2.6 1.5 2.2
UK | Long-term growth rate      
Impairment losses      
Change in assumption that would lead to impairment (2.8) (1.4) (2.1)
UK | Projected adjusted EBITDAaL CAGR      
Impairment losses      
Change in assumption that would lead to impairment (5.6) (2) (2.9)
UK | Projected capital expenditure      
Impairment losses      
Change in assumption that would lead to impairment 10.3 3.3 4.9
Romania      
Assumptions used in value in use calculation      
Pre-tax risk adjusted discount rate   11.00%  
Long-term growth rate   2.50%  
Projected adjusted EBITDAaL (as a percent)   1.50%  
Bottom of range [member] | Germany      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent) 19.50% 17.60% 17.40%
Bottom of range [member] | UK      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent) 10.90%    
Bottom of range [member] | Romania      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent)   9.20%  
Top of range [member] | Germany      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent) 20.30% 20.70% 19.90%
Top of range [member] | UK      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent) 16.30%    
Top of range [member] | Romania      
Assumptions used in value in use calculation      
Projected capital expenditure (as a percent)   11.00%  
Base Case | Germany      
Assumptions used in value in use calculation      
Amount by which unit's recoverable amount exceeds its carrying amount € 0.3    
Recoverable amount less carrying amount   € (4.4)  
Base Case | Romania      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount   (0.2)  
Decrease in discount rate by 0.5 pps | Germany      
Assumptions used in value in use calculation      
Amount by which unit's recoverable amount exceeds its carrying amount 3.2    
Recoverable amount less carrying amount   (1.7)  
Decrease in discount rate by 0.5 pps | Romania      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount   (0.1)  
Increase in discount rate by 0.5 pps | Germany      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount (2.2) (6.6)  
Increase in discount rate by 0.5 pps | Romania      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount   (0.2)  
Decrease in EBITDA by 2 pps | Germany      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount (3.1) (7.6)  
Decrease in EBITDA by 2 pps | Romania      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount   (0.2)  
Increase in EBITDA by 2 pps | Germany      
Assumptions used in value in use calculation      
Amount by which unit's recoverable amount exceeds its carrying amount € 4.0    
Recoverable amount less carrying amount   (0.8)  
Increase in EBITDA by 2 pps | Romania      
Assumptions used in value in use calculation      
Recoverable amount less carrying amount   € (0.1)