Advice on transfer of shares from an Employee Stock Purchase Plan to UK broker.

I'm after some advice...I have around £8K worth of US stock purchased via an ESPP and received a letter from CPM (the ESPP administrator) advising that I need to sell or transfer it to a broker. I have a fund & share acc with HL and have not yet invested in an ISA this year.

Can anyone advise on the best route for me to go down? I'm assuming to transfer to a stock & shares ISA, but not sure how to or which to go to? I also want to avoid paying tax twice, which apparently can happen. Thanks!