Кроме основной нормы 18 % для основного пула (main pool), используется специальная норма 8 % (special rate).

Rates and pools
If you’re claiming writing down allowances, group items into pools depending on which rate they qualify for.

The 3 types of pool are the:

main pool with a rate of 18%
special rate pool with a rate of 8%
single asset pools with a rate of 18% or 8% depending on the item

Кстати, нашел еще один вариант перевода writing down allowance (WDA)

WDA - налоговая амортизация

https://www.cimaglobal.com/Documents/Our locations docs/Russ...

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Note added at 52 мин (2018-12-27 11:46:47 GMT)
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https://www.gov.uk/work-out-capital-allowances/rates-and-poo...