Can someone tell me which spider this is please? I've found a few of them in my home in North-London, are they poisonous?
Very nice, indeed! This is a Spitting Spider (one of the Scytodes species, but I'm not sure which is most likely over in the UK). That's a good photo, by the way. This spider is easily told in the wild by its odd-shaped, domed carapace, with the 'Rohrschach-blot' design around the edge, and the spindly, banded legs. It's a slow-moving, very mild-mannered spider, with one of the more fascinating methods of catching prey: basically it spits a sticky saliva in zigzags that restrains the potential food, then rambles up and bites it. I include a photo and a couple of links for your enjoyment - using a familiar species from the US, Scytodes thoracica.