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Accounting policies (Tables)
12 Months Ended
Dec. 31, 2021
Text block [abstract]  
Estimated Useful Lives of Property, Plant and Equipment Depreciation on other assets is calculated using the straight-line method to allocate their cost less their residual values over their estimated useful lives as follows:
Buildings (freehold):
   20 – 50 years
Buildings (leasehold):
   over the period of the lease
Plant and equipment:
   3 – 10 years