Many thanks for the quick response - we'll move it out into the garden then.
At the risk of sounding rude (for which apologies in advance), you are pretty sure on this? I know very little about spiders, but my girlfriend got bitten in Langkawi and swelled up quite badly so I shall have to reassure her we shouldn't just squash it!
No need to apologise. I'm sure it's a Tegenaria, but I can't give total assurance on the effect of its poison. On most people it wouldn't have much effect (I've come across one or two people who've been bitten). The NHM don't include it in their web page on spiders that can cause nasty bites - see http://www.nhm.ac.uk/nature-online/life/insects-spiders/identification-guides-and-keys/spider-bites/.
However, just like a small minority of people are badly affected by bee or wasp stings, so some might react badly to being bitten by a house spider.
If you let it free in the garden it will probably live happily under the shed without you being aware of it and even if you squash it there are probably plenty of others in your general environment.