Came across this spider on the kitchen floor tonight, it then returned to its web on a disused cabinet standing against the wall. Haven't seen this type previously indoors; the kitchen is pretty chilly.
This is a male Steatoda nobilis (noble false widow). Females are quite sedentary, so even if found indoors they aren't necessarily a problem if they have made a web out of the way (I still don't like them in the bedroom/bathroom). Males, as you have seen, wander around more (in order to find a mate). Because of this, it might be a good idea to put him outdoors, should the opportunity present itself.
Males don't feed when mature, they only live for a season/year, so he's on borrowed time anyway. Neither males, nor females are aggressive, they're pretty docile. Bites only usually occur when the spider is inadvertantly squashed against the skin, the spider's venom is not dangerous to humans.