Be mindful that different platforms charge differently. Some on a percentage basis and some only per deal made. Obviously if you’re throwing it all in via an ISA transfer and investing in one go then that is very different from drip feeding. Many worship at the altar of Vanguard and go direct to them forgetting their funds are available via other platforms at less cost. And obviously if you go to vanguard direct you are limited to their funds and cannot do individual stocks.
These links might help you decide.
https://monevator.com/compare-uk-che...nline-brokers/
https://monevator.com/compare-the-brokers/