This is a mature male example of Steatoda nobilis, all you need to know is explained here: http://www.nhm.ac.uk/nature-online/life/insects-spiders/false-widow/index.html
But I am intrigued as to where you found it.
Ok thanks. I awoke last night to go to the loo (apologies again) and felt something moving beneath my T Shirt, I panicked and grabbed where I felt the movement and killed him. My fear now is that I have a 3 month old baby sleeping in the same room, should I be worried? I realise there is a lot of panic around at the moment and that bites are rare but my baby is mega important to me. Thanks for any advice!!
I can't guarantee that one of your family won't be bitten, but it's still very unlikely. Sounds like you have come fairly close with one down your shirt - so I would like to think that that lengthens the likelihood of another incident. Now you know what they look like keep an eye out and remove any you find indoors; that's about all you can do.
Thanks so much for the information and reassurance, my partner wanted to head straight for a hotel and sell the flat tomorrow. You may have just saved me a fortune! Lets hope we all sleep well tonight.