BIM84135 | Averaging: marginal relief
From HM Revenue & Customs · Business Income Manual
S223(4) Income Tax (Trading and Other Income) Act 2005
Marginal relief gave some measure of profit averaging when the volatility figure fell between 70% and 75%.
Marginal relief was repealed in Finance Act 2016 and the last year this relief could be claimed for was the 2015/2016 tax year.