If you have an existing ISA – either a Cash ISA or a S&S ISA – you can transfer it to another provider. So if you have £5,000 in a Cash ISA and want to move it to your Vanguard S&S ISA, you can go into your Vanguard account and select “transfer” to begin a transfer in. Equally you may have a S&S ISA somewhere and be unhappy with the fees or choice of funds, and again you can transfer it.

Some Cash ISAs may have lock-in periods for a guaranteed interest rate, so you may have to wait to be able to transfer, or lose interest.

Transfers aren’t new contributions, so they don’t use up your annual contribution allowance. You can move a £5,000 Cash ISA into your S&S ISA and still have £20,000 of allowance remaining that year for new cash to be contributed.