For some reason when I see a game on sale it is at a lower price but once I click the game and get taken to it's page then the price goes up about £2. What's going on?

The £2 difference is big enough to make me not want to purchase the game.

more details would be helpful, what game do you try to buy?

Well It's happening for multiple games, when I click on a bundle on the GoG homepage it shows the price of each game in the bundle but when I click on the game itself the price goes up.

The prices you see first are the price of the game if you buy the whole bundle. As you take games away from your purchase the price goes up.

many bundles have extra discounts. if you purchase every game that you don't own from one bundle, then you get the full discount. for example:

all fallout games at once -> 50%

only one fallout game -> 40%

Ah, I started to suspect that was the reason after a while. Thanks for clearing that up both of you.

This is actually a 'New to GOG tax' that GOG applies to all new users. Once you have a year on GOG, the price goes down and continues to fall with each subsequent year here. I anticipate GOG paying me to take games in the near future. :P