Hi
If your other income (income not from savings and investments) is less than £17,570 you will be eligible for a 'starting rate for savings'. The maximum starting rate for savings is £5000, every pound of other income you have that exceeds your annual Personal Allowance reduces your starting rate for savings.
For example, if your Personal Allowance is £12,570, it will be used up by the first £12,570 of your income.
If the total of your other income is £13,875.68, the remaining £1,305.68 (£13,875.68 minus £12,570) will reduce your starting rate for savings by £1,305.68.
Your remaining starting rate for savings is therefore £3,694.32 (£5,000 minus £1,305.68)
If you go over your allowance and receive a pension or are employed, HMRC will change your tax code so you pay the tax automatically. However, should your income from savings and investments exceed £10,000 you will need to register for Self Assessment.
Please see the guidance here:
Tax on savings interest