You are taxed on the interest on your savings when it is accessible by you. So if you pick a fixed-rate savings account that pays out all the interest at maturity, for tax purposes all of that interest will be counted in one tax year.
Investing wisely is a core component of your financial security, and with this in mind, making use of your Individual Savings Account (ISA) and pension tax efficient allowance can be vital in helping to retain more of your wealth while keeping it away from the taxman at the end of each financial year.