Everyone in the UK over 18 has an annual £20,000 ISA allowance (for the 2021/22 tax year ending 5 April 2022). You can choose to use all of this for a Cash ISA if you want, or you can split it between stocks & shares and any of the other types of ISA: Cash ISAs, Lifetime ISAs and Innovative Finance ISAs. OakNorth currently only provides Cash ISAs.