Tax on allowances depends very much on which tax office your employer uses.
Southend tax office didn`t tax allowances at all.
BA crews pay up to 41% on allowances
BM/ KLM UK sorted out a deal one year where tax was 26% on allowances. There tax offices said if a deal was not sorted out we would get taxed at 100%. This was because the tax office wanted to tax BM/ KLM UK crews the same as BA crews at 41%. BM cabin crew were on £1.07 an hour at the time!