Andy, yours is a female example of the Noble a False Widow, Steatoda nobilis ... well an ex one by the look of it.
For more info. on False Widow spiders please see these links:
Thanks for the quick response, is there anything I should do to avoid being bitten? as I found this one under a book which was on my bed, and I dont fancy one interrupting my sleep haha
Amaurobius are the most common genus of spider that I see inside my own home (more than one a month, but be aware I don't deter them & do look for them). I have even woken up with a big fat female crawling over me. I don't particularly like them, but I have never been bitten by one. They can bite, it does happen very occasionally if trapped in clothing etc., but this is only likely to result in a some aching & swelling for a couple of days.
If you want to keep numbers down, don't get rid of any daddy long legs/cellar/skull spider (Pholcus phalangioides), these just love munching on Amaurobius & other big hairy spiders.