Cash isa

[beerandpopcorn]

If I take out a 20k isa with this years allowance will it be possible to later
transfer it to an investment isa?
What I mean is do I have to wait until after the 'locked in' period.

Hope that makes sense

Yes, you can transfer from cash ISA to stocks and shares ISA, and vice versa.

www.moneyadviceservice.org.uk/en/articles/stocks-and-shares-isas

^You can transfer money from a Cash ISA to a Stocks and shares ISA.
If you transfer an ISA that you have paid into during the current tax year to a new provider, you must transfer the whole balance. For ISAs from previous years, you can choose how much to transfer.^

What do you mean by 'locked in period'? If it is a fixed term cash ISA you will have to wait until the end of the term or transfer early (if allowed) and pay the exit penalty (equivalent to loss of interest for a set period). I'm not sure they allow early closure by transfer to another ISA, they may just repay it to you as normal cash.