Hi Drippy,
Welcome to the board! I am also located in the UK, and can recommend a few brands and places to get them.
Check out
www.incontinencechoice.co.uk - they have a great sample service. The only problem is that most of their products are unsuitable for overnight use (in my experience). One of their best performers is Abena Abri-Form Premium. That one is cloth backed, which is a disadvantage in my opinion. Abena makes a plastic backed version, but this store does not stock it. One interesting thing about them is that they list a pretty accurate absorption level for each of their products (in mL, instead of the highly subjective "drops").
I would normally recommend
www.incontinenceshop.com - but they have been having problems keeping items in stock. When questioned about restock times, they will give an inaccurate estimate and then change the story when they fail to meet the stated date. I have a feeling they are going under. They normally stock BetterDry, which is an outstanding overnight diaper. Sadly, they are out of stock and seem to have removed them from the site. They also stock the plastic backed Abena (when they have them).
If you can find plastic backed Abena or BetterDry, they are definitely worth a try.
Probably the best supplier in Europe is
www.saveexpress.de - they have all the premium brands. The site is in German, but there is an English option.
Good luck in finding the product that works best for you. I am available to help in any way that I can.