It would be Steatoda bipunctata for my money - AKA the 'Rabbit Hutch spider'.
This is the most common and widespread of our six UK False Widow species. The common name comes from their love of sheds and outbuildings, including rabbit hutches, and I doubt that there is a rabbit hutch or shed in the land that does not have this spider in residence.
It is a very common garden species throughout the UK and is not a species implicated in bites as other members of this group are.
For more False Widow information please see the flowing links: