If you are using T3 there is no scanner at Fast Track. That is also the lane used by those requiring ground assistance ie wheelchairs. If you are flying from T5 there are scanners now back at north and south but again Fast Track generally avoids those.

They don't take those visibly unable to use the scanner, in my experience. But when asked by someone in a letter the response was that if one was unable to raise ones arms, one does the best they can.

I think that more Americans worry because they are used to scanners being primary at so many airports now in the US, with no WTMD. It isn't that way here; the scanners are often not even turned on or in operation, and very very VERY few people are ever selected. Diabetics fly out of LHR every day and I have never read of anyone reporting an issue, and I do regular searches for such information.

And what 'horrible health insurance'?! Do you mean the very poor situation in the US for health insurance? I'm confused by that.