Hard to be sure, but from what I can make out of the markings I'm inclined to say it's a False Widow Steatoda nobilis or its close relative, the Rabbit Hutch Spider Steatoda bipunctata. You might be able to confirm this one way or the other by comparing it with the pictures here:
The exact shape and contrast of the Steatoda nobilis markings varies but they generally have a pale band across the front of the abdomen and extending along the sides, and light pattern in the centre on the top.
The rabbit hutch spider isn't of any genuine concern regarding bites.
Males wander when looking for a mate in Autumn, but females from what I've observed tend to just hang out near their established web for ages, keeping tucked away in a convenient refuge by day. I had one female hanging around near the bathroom window for weeks, and it never wandered.
Bites tend to occur when they feel physically threatened, eg. prodded, handled roughly or getting caught up inside clothing or bed sheets. They're quite happy to live outside - I've got several just outside the back door and they keep themselves to themselves. To be on the safe side I suggest you just put any you find outside.