Thanks everyone! I am glad you all seem to agree with me and I am certainly going to ask them to book me ex-LGW. I chose LHR simply because I live nearer LHR than LGW and on the return journey it is much less hassle driving home and I don't mind the extra flying time - can always sip champagne although there's a whole other thread!
It also appears (from checkmytrip.com) that not only has the service from LHR-IAH changed, but it now goes through Detroit, not Chiacgo...? I don't want to buy a Hummer!