Can I use the £1,000 trading allowance for a small side income?

The £1,000 trading allowance applies to your total gross trading income for the whole tax year, not per job — so you'd add up the catering income from every party across the year. If that total is £1,000 or less, you generally don't need to tell HMRC or declare it, provided you have no other reason to file a tax return. If it goes over £1,000, you can deduct the £1,000 allowance instead of totting up your actual expenses, and you'd pay tax on the remainder above that. You can't claim both the allowance and your expenses for the same trade, though, so if your real expenses are higher than £1,000 you'd be better off claiming those instead. Keep a record of the income either way, as HMRC can ask to see it.