Depends where you are in the UK?
Steatoda paykulliana isn't a native of the UK though they do get brought in on fruit (it's possible they are breeding, but thats not been confirmed)
Going to need photos I'm afraid - otherwise its blind guess work and sizes as well please, (excluding legs)
You could take a look here to see if you can see anything similar:
Thumbnails of spiders in NW_Europe Theridiidae Nesticidae,Gumfoot web, scaffold web or cob web spiders