So the UK is in good company with (anecdotally) the Ukraine and Kazakhstan in denying a choice in this.
There was a good albeit understated quote in [UK human rights organisation] Liberty's response to the Department for Transport 19 July 2010 consultation on the body scanners:
(Helen Mountfield QC and Professor Conor Gearty, Matrix Chambers, who gave their advice on this issue):
“If a person were compelled to consent to any form of search as a condition of flying, whenever the requirement to undergo it was introduced, however intrusive it may be, however discriminatory, and however arbitrary and unjustified, there might come a point where the consent could not be held to be ‘true consent’…”
(Comes up first in a Google search for "consultation 19 July scanners liberty"
I have looked for the outcome of that consultation that closed on 19th July last year, but can't find it. I would write to my MP (who's the only Green MP in the country, however, and who is likely utterly opposed to aviation full-stop) to see if she can ascertain why only the UK out of every other western country (barring Ukraine and Kazakhstan) deems it absolutely necessary to deny access to a flight (even if you also consent to a manual search, or even a strip search) if you refuse to be zapped. This ruling was put in place hurriedly in the dying days of the previous government, but the current government doesn't seem in a hurry to reverse it.
It's quite tragic, as I've noted on other forums, how people so readily accept this treatment. I can sympathise, however, given the arm-twisting option of "forgo your business trip/hard-earned holiday or go through this machine. It's your choice". I think London City Airport and even Southampton are now attractive options to Gatwick (I can see these machines being expanded to the South Terminal soon also without any announcement) ...