Interactive Brokers (U.K.) has been approved by HMRC to manage ISAs. WOW!!!

Now UK tax residents can deposit up to 20,000 GBP per year into tax-free account to trade international stocks. Gains, dividends are tax-free, instant withdrawals allowed any time.

IB would be the cheapest ISA provider in UK. We have had some old-fashioned brokers (e.g., HSBC) who charges 0.5% for fx conversion, 10 GBP per trade. IB charges 0.03%, 0.005 per share and give access to all markets.

I think you still have to pay 0.5% stamp duty on purchases, and you can’t hold foreign currency, but an interesting offer all the same.

you pay 0.5% only when you trade UK stocks
yes, you need to deposit GBP, but IB converts GBP to USD internally at 0.03% rate, to purchase assets and then converts back to sell asset
so in total you pay 0.06% per round trip I believe.

It would be better to convert lump sum into USD then you pay once fx spread.