You have a capital sum you want to save you for a special reason, your reason will be special to you

You could save in a cash isa, which may or may not be changed by the current chancellor. The interest you receive will be variable.

You could save within an isa, using a money market fund, where again the interest you receive will be variable.

Or you could buy a UK Government Gilt, where all gains are tax free if held within a tax free wrapper.

You want to save for 5 years and decide to buy

Cost to buy one unit currently £101.48, which matures on the 07/03/30 at £100.00

If you bought for example 10k of T30 the income yield will be 4.3%

£430.00 pa. If you re-invested the twice yearly payments into the gilt, considering the cost of re-investing maybe once a year.

After 5 years your 10k should compound @ say 4% p.a. into £11,700.

Interest rates will change during this time period but as long as you hold until maturity there is no risk as £11,700.00 will be returned which includes your capital investment of £10,148.00