This is an immature example of Steatoda grossa, sometimes called the Cupboard spider - so very much at home there.
Steatoda grossa is one of the more common and widespread of our False Widow spiders. This is a species that lives comfortably in the clutter of sheds and garages and will also live comfortably indoors in cooler parts of our homes.
It is not a species that is reliably implicated in bites.
For less shocking and hopefully reassuring information on False Widow spiders please see the following link: