for Foma only, fomafoto.com. Quite the best prices for Foma films & paper, even including delivery from Norway to the UK (and I expect ROI).
Slavomir (who runs it) is smart and efficient.
For Ilford, Kodak + Foma, CliffordStreetPhotography.com is worth a mention.
I've bought from
https://www.sharifphotographic.co.uk/ too, good service and friendly.
Otherwise, any of the UK/EU names mentioned are good. Maco/Fotoimpex often have good prices but delivery costs to UK/ROI can kill any advantage. I used to have a spreadsheet for all the popular films from all the usual UK suppliers so I could compare. Really there isn't much to choose between them once you count in delivery costs for "normal" amounts of film - say 10 or 20 rolls.
If you want to buy in large quantities then ask for price breaks from any of them.
There are so few retailers now that they can't really afford to offer poor service (because competition is so tight), and I've bought from many of those UK retailers mentioned so far and had no problems and only good things to say. There is one I'll never buy from because of the proprietor's rudeness to me, despite their having a few things unobtainable elsewhere.
Sometimes the same retailers have offerings on not only their own sites but eBay and Amazon, and there are occasionally significant price differences between them!
I've got a soft spot for RK who are always friendly and extremely helpful.
Buying from the US often seems appealing because the prices can seem incredibly low compared to UK prices, but once you factor in delivery, import duties and VAT, smaller quantities can suddenly turn out much less of a bargain and often more than buying locally. But if you buy in bulk, it can still prove a bit cheaper. You have to do your homework.