There's a thread on the Rotorheads Forum which might be of interest - look for the post by Heliport.
http://www.pprune.org/cgibin/ultimatebb.cgi ?ubb=get_topic&f=11&t=001397
I went on one of the flights last year which included flying @ 800' across LHR - the best view I've had of the airport even though I've been based there for years.
Highly recommended!
[ 22 August 2001: Message edited by: virgin ]