I’m UK based and just starting to look seriously at paid marketing options too.
As far as I’m aware, the ban on gambling advertising on Google, Yahoo etc covers the UK as well. If they have relaxed that following on from recent UK regulatory activities, then that’ll be interesting…but i suspect you’d then need to follow the UK gambling advertising guidelines (can get you a copy if needed)
I’ve had limited success with abcsearch, they allow gambling ads and geo-targetting to UK.