caculating my 1 year working expiration date

Hey guys!

I have been in the Uk for about a year now, working. I can still stay, without working until June 2010, but will soon have run out of time on the work part of my visa.
However, I am not exactly sure how much time I have left to work. I generally know how much time, but want to make sure my predictions match up with the official recording.
My question is: how do i find out how much time I have worked officially here? Where do I go to retirieve this information, so I don't accidentally work over the 1 year mark and get introuble/deported??

I'm in London, so if I can go somewhere in person to get this info, I would prefer that, but will do whatever I need to!

Thanks,
Samantha