Apart from the odd house spider I've rarely seen many spiders up there and never one like this. This one had a body between 10 - 12mm and was dark brown in colour. Looking at the distribution maps this hasn't been recorded there before.
Just to clarify the spider was crawling around on the outside of the door rather than inside the shed. It wasn't in a web. The spider was very distinctive and it was the shape of the abdomen that made me think it was this spider. I tried to look for it later on to take a picture but it had wandered off. Fine looking spider though.
BTW are the house spiders moving north, I've been going to Scotland for 25 years and never really saw them there until about 10 years ago. Now there are a lot if my mother in law's shed is anything to go by.