This is one of the False Widow Spiders, the Rabbit Hutch Spider Steatoda bipunctata, for it is commonly found near or in human habitation such as outbuildings or sheds. They are called False Widow Spiders for they are commonly mistaken for the real thing which are not found in the UK, unless accidentally imported, which is rare.
I found this one in a sack of potatoes which I had been keeping in the garage.
Double click on images to enlarge.
May 2018, rear garden, Staffordshire, England. © Pete Hillman