It seems they didn't actually put a reserve on the listing and i have won it it for £70. But it the description it says reserve of £90. Does this mean they can refuse to sell it to me? (Collection only)
they shouldn't refuse to sell it to you but they probably will. Just email and ask when you can collect and see what they say.
I guess they didn't put an actual reserve on to the auction, but stated it in the description only?
If that is the case they have made a mistake and should sell to you at the price you won at. But if they refuse all you can do is report them as a non performing seller. There is nothing you can do to force them to let you have it at that price - but if they refuse you then they will get a strike against them.