If they suspect you've done anything illegal (or quasi-illegal) then they'll freeze the money and you may end up needing a lawyer to get it back, certainly will take ages and be a right PITA anyway, it happened to one crypto guy I deal with, took over one year, to get the money out but fortunately in all my cases they just gave me 6 (or 3, forgot which now) months notice that they'll close the account (not because they like you, but they are obliged to), in the UK you can complain to the banking ombudsman, but they are toothless and do FA, in the mean time you can carry on using the account as normal and drain it before the end or they'll just send you a cheque.

The best I found is to go to another bank and say that you're dissatisfied with your old bank and want them to close the account for you and transfer it to them, direct debits, standing orders, contacts and all, they all love to do this and some even reward you, ie Halifax gave me 100 quid opening bonus, it's a small way to get back a little at your old bank.

One though only gave me only six weeks or something, an Isle of Man offshore bank, so I asked them if it was OK to continue to use the account normally until then, they said yes, I then said that I'd send my Bitstamp balance to them (a lot at the time), that freaked them out and they almost pleaded with me to not send any more from the Estonian bank and gave me much longer to GTFO, in fact extended it twice as it really took some time to organise a bank that could accept the Bitstamp funds I needed for a property purchase that I'd already committed to.