This is nonsense, account size (spread bet size) doesn't change the pip value but it changes the spread itself. Regardless of the spread, the pip value is still the same.
ActivTrades offers 1:1 leverage and it's available in the UK and it's an FCA regulated broker.
Here's the info:
https://www.independentinvestor.com/spread-betting/brokers/
https://www.activtrades.com/en/shares-trading
So there's no commission and no overnight charges.
It really depends on what stocks you want to trade. All CFD brokers allow to trade popular shares.
Overall, stock offerings vary so you need to check with your preferred broker if they offer the shares you want to trade. I think IG and Spreadex offer lots of stock CFDs.