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Staff numbers and costs - Government grants and assistance (Details)
€ in Millions, £ in Millions
12 Months Ended
Mar. 31, 2021
EUR (€)
Apr. 30, 2020
GBP (£)
Mar. 31, 2020
Mar. 31, 2019
Disclosure of detailed information about borrowings [line items]        
Payroll supports received amount | € € 84      
Interest rate percentage (0.26%)   0.73% 0.01%
Debt Acquired Under HMT And Bank Of England CCFF        
Disclosure of detailed information about borrowings [line items]        
Unsecured debt from syndicated bank facility | £   £ 600    
Interest rate percentage 0.46% 0.44%