Found this little blighter lurking in a dark corner of the house near ground level. Never seen one before, though googling suggests steatoda grossa - however, I'm no expert and would prefer the opinion of someone better informed!
The body was about 10mm long (including the head) and reddish brown (looked slightly lighter in real life), dark legs. Three white triangular marks in a line down the back, a white line curving round the front of the abdomen, and other spots on the sides. The web was just a tangle of threads. I caught it with a glass and piece of card - it tried to run away, but once caught acted aggressively. I took it to the local park and released it in a sheltered spot.
Yes, you are correct, it is Steatoda grossa (AKA cupboard spider).
They do like lurking in dark corners, largely going unnoticed for this reason.
I'm surprised it acted aggressively, I see wandering males semi-regularly & usually try and contain them in order to take pictures - they don't make great models, always escaping - is it possible that the spider was just keen to get out of the glass, rather than actually "attack"? The ones I have let loose usually bolt straight for cover, rather than charge at me.
Thanks very much! On reflection it may well have been just a particularly energetic escape attempt - once released it certainly made no threatening movements, just scarpered. (You're right about them not being great models - it was a nightmare trying to get decent pictures of it!)
I'm used to the 'daddy long-legs' spiders, and the occasional house spider so it was a bit of a surprise to see an unfamiliar 'interloper'.