Yep, its a false widow. Looks like Steatoda nobilis to me. They get a bad press, but they're nothing to seriously concern yourself over.
THanks for your help. It's in the conservatory in the corner, It's been there for a couple of months and sits in full view on its funny looking web. Could there be more and should just leave it there?
You are very welcome.
There may be more, but unless you have other funny looking webs in the area, you probably don't.
I tend to let them be, I relocated a wandering male from my bedroom once, but if your one is just hanging in the conservatory, i'd just leave it there. Good pest control, it may even stop you getting bitten by a mosquito!
Sage advice from malthusius - I usually relocate any I find indoors but there will enevitably be others around the outside of the house and sheds/greenhouses. They really love conservatories and females will stay put and do not wonder - they will live comfortably for 2-3 years. They are indeed good pest control and we are surrounded by them (in southern counties at least) - a very few cases of people being bitten are reported and very often make the press, but this is not regular behaviour. They are strongly synanthropic and I have never found one that has not made its home on a man-made structure - we appear to provide perfect habitat and our change inn climate has suited them too.