To be able to claim tax relief on the money you add into your pension (such as the 25% bonus), you’ll need to be:
If you’re unemployed, you’ll still be able to add £2,880 to your pension per tax year, and the government will add 25%, which is £720.
‘Relevant UK earnings’ is things like your employment or self-employment income, but not including things like rental income or dividends (companies paying you some of their profit as an owner).
There’s also an annual allowance for how much you can save each year (typically up to your annual income or £60,000, whichever is lower).
Note: your actual tax treatment will depend on your individual circumstances.