As of 6th of April 2017, if you’re a freelancer with income from your business of under £1,000 a year, then you don’t have to register for Self Assessment with HMRC, or pay tax on your business income.

If your income is over £1,000 a year, you still have to register with HMRC, but you can use either the trading allowance of £1,000, or your actual business expenses and capital allowances, against your income to work out your profit. You can’t use both the trading allowance and your actual costs against your income - you have to use one or the other. 

The trading allowance isn’t available to partnerships, partners, or limited companies.