I'm in the UK. Buying crypto isn't banned, however trading is. I
You are the owner of the money and I don't know why you have to bend to the bank policies since you are from the UK. Why do you change bank just as Welsh said cause I read that Barclay, Natwest, SCB, RBS, TSB supported crypto related payment.
You can also also open Revolut account if you don't want leave the bank though.
To be fair to my bank, I've not yet tried to move money to a broker or any other route that might suggest 'this customer is buying crypto' so I can't comment yet as to whether they would block my account. However I'd rather find legitimate ways to avoid even highlighting this to them.