http://news.bbc.co.uk/1/hi/england/sussex/7725378.stm

I phoned a mate at Cornwall WT and he reckons that the false black widow spider (Steatoda grossa) is becoming more numerous due to milder winters not killing them off.  They're apparently native to the UK but have been relatively uncommon until about 15 years ago and are seen regulularly in the South now.

Maybe I should have added this to the Global Warming thread.  :-\