Morning how can I transfer the interest gained on last year’s cash isa into this year’s cash isa?
There is no such thing as “last year’s Cash ISA”. If you earned interest in the last tax year then it will arrive in your account this tax year.
If you mean “can I transfer the cash from a previous ISA to my current ISA” then yes, but make sure it is done using your new provider’s transfer ISA process. If you withdraw cash then you will have to use this year’s ISA allowance to deposit it in your current cash ISA,
Are you looking to move that interest so it counts as a new deposit for this year’s ISA allowance?
If the interest is already inside your ISA, it’s actually better to leave it where it is. Any interest earned stays tax-free and doesn’t use up your new £20,000 annual limit.
The only way is to withdraw it and then pay it back in, then it will count that as a new deposit, which means you’d be using up this year’s allowance for money you already had tax-protected!