Property, plant and equipment - Disclosure of analysis of property, plant and equipment (Details) - GBP (£) £ in Millions	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	£ 64,433
Property, plant and equipment, ending balance	68,907	£ 64,433
Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	81,813	73,340
Exchange adjustments	(976)	2,405
Additions	7,167	6,853
Disposals	(465)	(654)
Adjustment for change in discount rate on decommissioning provisions	29	(48)
Reclassifications	(169)	(83)
Reclassification to held for sale	(266)
Property, plant and equipment, ending balance	87,133	81,813
Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(17,380)	(15,808)
Exchange adjustments	199	(506)
Depreciation charge for the year	(1,804)	(1,765)
Disposals	438	592
Reclassifications	166	107
Reclassification to held for sale	155
Property, plant and equipment, ending balance	(18,226)	(17,380)
Land and buildings
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	3,272
Property, plant and equipment, ending balance	3,452	3,272
Land and buildings \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	4,066	3,659
Exchange adjustments	(49)	126
Additions	59	158
Disposals	(55)	(163)
Adjustment for change in discount rate on decommissioning provisions	0	0
Reclassifications	277	286
Reclassification to held for sale	(88)
Property, plant and equipment, ending balance	4,210	4,066
Land and buildings \| Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(794)	(773)
Exchange adjustments	10	(30)
Depreciation charge for the year	(80)	(122)
Disposals	50	127
Reclassifications	(3)	4
Reclassification to held for sale	59
Property, plant and equipment, ending balance	(758)	(794)
Plant and machinery
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	53,839
Property, plant and equipment, ending balance	57,821	53,839
Plant and machinery \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	69,765	63,022
Exchange adjustments	(841)	2,073
Additions	1,157	1,196
Disposals	(271)	(331)
Adjustment for change in discount rate on decommissioning provisions	29	(36)
Reclassifications	4,725	3,841
Reclassification to held for sale	(13)
Property, plant and equipment, ending balance	74,551	69,765
Plant and machinery \| Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(15,926)	(14,441)
Exchange adjustments	177	(444)
Depreciation charge for the year	(1,515)	(1,459)
Disposals	252	311
Reclassifications	281	107
Reclassification to held for sale	1
Property, plant and equipment, ending balance	(16,730)	(15,926)
Assets in the course of construction
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	6,705
Property, plant and equipment, ending balance	6,955	6,705
Assets in the course of construction \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	6,760	5,587
Exchange adjustments	(67)	156
Additions	5,754	5,345
Disposals	(5)	(4)
Adjustment for change in discount rate on decommissioning provisions	0	(12)
Reclassifications	(5,389)	(4,312)
Reclassification to held for sale	(31)
Property, plant and equipment, ending balance	7,022	6,760
Assets in the course of construction \| Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(55)	(60)
Exchange adjustments	0	0
Depreciation charge for the year	(20)	(1)
Disposals	2	2
Reclassifications	0	4
Reclassification to held for sale	6
Property, plant and equipment, ending balance	(67)	(55)
Motor vehicles and office equipment
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	617
Property, plant and equipment, ending balance	679	617
Motor vehicles and office equipment \| Cost
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	1,222	1,072
Exchange adjustments	(19)	50
Additions	197	154
Disposals	(134)	(156)
Adjustment for change in discount rate on decommissioning provisions	0	0
Reclassifications	218	102
Reclassification to held for sale	(134)
Property, plant and equipment, ending balance	1,350	1,222
Motor vehicles and office equipment \| Accumulated depreciation
Changes in property, plant and equipment [abstract]
Property, plant and equipment, beginning balance	(605)	(534)
Exchange adjustments	12	(32)
Depreciation charge for the year	(189)	(183)
Disposals	134	152
Reclassifications	(112)	(8)
Reclassification to held for sale	89
Property, plant and equipment, ending balance	£ (671)	£ (605)

The amount of additions to property, plant and equipment other than those acquired through business combinations. [Refer: Business combinations [member]; Property, plant and equipment]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The decrease in property, plant and equipment through classification as held for sale or inclusion in a disposal group classified as held for sale. [Refer: Disposal groups classified as held for sale [member]; Property, plant and equipment; Disposal groups classified as held for sale [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of depreciation of property, plant and equipment. [Refer: Depreciation and amortisation expense; Property, plant and equipment]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The decrease in property, plant and equipment resulting from disposals. [Refer: Property, plant and equipment]

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The increase (decrease) in property, plant and equipment resulting from net exchange differences arising on the translation of the financial statements from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Property, plant and equipment]

+ References

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- Definition

The increase (decrease) in property, plant and equipment resulting from transfers. [Refer: Property, plant and equipment]

+ References

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-Name IAS
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- Definition

The amount of property, plant and equipment including right-of-use assets whose underlying assets would be presented as property, plant and equipment if they were owned. [Refer: Property, plant and equipment; Right-of-use assets]

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- Definition

Increase (Decrease) Through Adjustment For Change In Discount Rate On Decommissioning Provisions, Property, Plant And Equipment

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