Self employed – If gross income is over £1,000
Partner – If gross income is over £1,000
Rental income – If net rental income is over £2,500
Income from dividends or savings & investments – If over £10,000
Claiming tax relief on expenses – If expenses are over £2,500
Minister of Religion
If you or your partner claims Child Benefit and your income is over £50,000
If you have a CGT liability
Note re penalties for late submission of tax return
If HMRC require you to submit a tax return, they must formally request one in writing. Normally they do this in the April following the end of the tax year. If they do this, and you do not submit it by the following 31 January (for online returns), you will incur penalties. These can ramp up quickly. If you have not submitted it by 31 July, the penalties will be at least £1,300.
However, HMRC can’t charge penalties if they have never formally requested a tax return. Even after they finally do request a return, you always have 3 months to respond before penalties start to apply.