There are a number of Steatoda species found in Britain, all so-called 'false widow' spiders. Three are possible in or near buildings, S. bipunctata (very widespread), S. grossa (widespread and sometimes very frequent in the southwest, but becomes much scarcer further north and east, but in the last few years seems to be increasing) and S. nobilis, the one which gets the press for biting humans (originally confined to the south coast, now increasingly turning up elsewhere in southern England and found in 2006 in Barry, S. Wales). You can see the known Essex distribution at Species+Account/s/Steatoda+nobilis and nationally at http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Steatoda+nobilis
I can't be sure which false widow you mean, but I am guessing you think it was Steatoda nobilis. Can you post a picture which shows the abdominal pattern or email a picture to me (see email link for Peter Harvey at http://www.essexfieldclub.org.uk/portal/p/County+Recorders ) so that I can be sure which false widow you have found. I would also appreciate a postcode or map grid reference so that your record can be added to the recording scheme.
Steatoda nobilis has on occasions been responsible for bites, even though many of the cases publicised for this are almost certainly due to another cause. Most 'spider bites' have other causes and the media do not present an accurate or sensible story. Generally speaking people are vastly more likely to be stung by honey bees or social wasps, and spider bites are very rare. Steatoda spiders catch their prey using an untidy 'scaffold' web in corners, under window ledges etc and are generally unlikely to leave the webs to wander around, except when the males become adult and are looking for females.