I have read that Kraken withdrawal fee is cheap but I have not used the exchange before. I do not know about the trading fee.
I prefer to use OKX for bitcoin withdrawal. I think OKX is allowed in UK?
But if you are not the person that trade often but in just few time and you want your coins to be in your wallet after each trades, you can use
http://exch.cx/. The exchange also support lightning network.
For small amount and if you are willing to use lightning network. Binance, BitMart, OKX, Kucoin, Bitget and some other exchanges have lightning network payment.