See para 69:
https://www.bailii.org/uk/cases/UKUT/TCC/2019/167.html
Very embarrassing for the appellant’s counsel that this point was not even argued (it is fairly well known)! See also:
https://www.step.org/news/claiming-tax-relief-small-employment-related-e...
https://www.taxjournal.com/articles/online-tax-rebate-v-hmrc
https://www.taxation.co.uk/Articles/was-a-company-a-tax-adviser-for-mlr-...