I've already been lucky enough to go on a trip to the Heathrow Control Tower Building, and so I won't put my name down for this one.
It's a very interesting experience, so I'd urge anyone that could get there to put your name down and go for it.
Some pictures from my trip here:
http://www.eludlow.flyer.co.uk/egll/index.htm
I found the radar rooms particularly interesting (especailly the SVFR controller).
We were lucky enough to get a visit to the glasshouse, so you never know, you may get lucky.....?
tKF