What you have found, Fg Off Max Stout, is that most people in the U.S. flight training business don't understand the Visa regs, don't want to understand the Visa regs, don't want to read an email from you (or anybody else) longer than about two lines which rules out any meaningful discussion on the subject, and prefer to hide behind the "M1 is mandatory" position.
Yes, most U.S. Part 61 schools will happily accept your training request, causing you to waste the TSA fee. They are not dishonest, just ignorant of the foreign student situation.
There isn't a lot you can do about it. Just get your writtens and medical here, pop over to Farnborough and get fingerprinted, allocate a day wasted at the US Embassy in London, and it's all fairly painless.
But be prepared for an extended interrogation on future visits to the USA, due to the M1 visa having once been issued.