Depending on where you are in the country, these spiders can relatively common. They prefer cooler, darker places & are more easily surprised in sheds & garages...I have them in my home & only usually see wandering males. They can be very elusive in areas of high footfall and mostly go completely unnoticed.
They are commonly known as the cupboard spider, but are one of the false widow species - Steatoda grossa. I wouldn't be overly concerned about bites, they can, but they are typically very shy & avoid us where possible...be aware of them, but no real need to fear them.
Sorry that would have helped I am in Hertfordshire. Hmm don't like that news but thank you. I am moving and have packed the garage don't really want to take any with me or worse hey migrate from my moving boxes in to my indoor moving boxes in the van!!