OWC has memory selectors to help find correct RAM. Crucial too.
Newegg.com also has RAM selectors to find memory for your model laptop
I have had good experiences with G Skill and mushkin off the top of my head. Gskill in my personal machines......
Once you know the speed and specs of RAM i have found RAM for macs in the non mac memory sections at a better price.
Plenty of user reviews for memory and other products on newegg.com.
2010 model MBP shouldn't have any problems finding quite a few selections for 8GB of memory.
Just noticed your link was for the UK..... even if newegg and other vendors i mentioned don't ship to the UK, I'm not sure if they do, newegg does have some strict rules about billing and shipping address for orders... anyway once you have specific model info for what you want to order, you should be able to find a seller, for what you need in the UK if not able to order from the wesites i mentioned above.