I am calculating 'reasonable' allowable expenses for my UK tax return in good faith, but the advice from HMRC's internal guidance seems limited. I have looked online and advice from accountancy experts seems highly contradictory, in terms of what is allowed and your method of calculation. My figure potentially won’t be much more than the £1,000 trading allowance, maybe £1,100 - £1,500 at most. If HMRC queries this and states that I have overestimated and indicates that I could only claim, for example, £600, am I correct in thinking I cannot then revert to the trading allowance retrospectively? Is it therefore wise to go with the trading allowance and save myself a load of hassle and maybe even cash? 

Arthur replies: 

Unfortunately, your question is not clear to me. But I can tell you the following. Where the total receipts from all trades plus any miscellaneous income in the tax year are no more than £1,000, the allowance is given automatically in full so that no tax is payable and the income does not have to be declared. Where the total receipts from all trades plus any miscellaneous income in the tax year exceed the £1,000 allowance, an election can still be made for partial relief, where the allowance is deducted from the receipts instead of the actual allowable expenses. This will clearly be beneficial if the expenses are less than the £1,000 allowance. The individual can decide how the £1,000 allowance should be split between two or more trades, or between trades and miscellaneous income.