The lakeland kit is a good one...
Yes they do sell white eggs here.
They also sell really neat blue eggs. Take a look for Rare Breed eggs next time you are in your larger supermarkets.
Brown eggs will need stronger colors.
Basically you take a separate cup for each color, dissolve about 8 drops of regular liquid food color, in 1 cup of hot water. Stir in about 1/4 cup of white vinegar and commence with the fun. You can use a white wax crayons to do designs or stickers or whatever comes to mind.
With brown eggs you also just get more muted tones.
If you goggle there are tons of recipes for natural egg dyes as well.
Lakeland is at:
http://www.lakelandlimited.co.uk/Also I have seen dye kits in other stores as well like Debenhams in the furniture/decor section of all places. Oh and Marks and Sparks too.