Probably though because the FAA has no concept of non IR'd or non "IRI" instructors teaching for an instrument "rating" (there is also no concept of an non instrument, instrument type rating under the FAA).
I don't think so. The FAA is well aware that all sorts of things go on in the rest of the world, and they make it clear what can be done by an authorised instructor (the very general definition) vs what needs an FAA Instructor. For example (and I don't know anything about military flying) but an ex-military pilot could have instrument training that wasn't by an ICAO IR qualified instructor but counted as instrument training by an authorised instructor. Probably a fairly common case.
You could claim to an FAA DPE that Compton Abbas to Henstridge was a cross courntry flight and he'd probably believe you....technically under the FARs it is not
This analogy is wrong, because you'd be making a claim that contradicts the explicit 14CFR definition of cross-country flight as >50nm. The whole point is that "instrument training" by an "authorised instructor" does not specify "ICAO IR qualified", it permits the more general case of instrument training (eg. my military example). A better analogy is whether the 40hrs of total instrument flight time is met by an IMC-r holder who has done solo hours in IMC after the training. Of course does - it is "instrument flight time" as per the 14CFR definition, because they don't define it as "exercised by the holder of a valid ICAO IR". And, again, it's not a UK IMCr loophole - the same can apply to military flight time, or a holder of Australia's PIFR qualification etc.
better to be safe than sorry
You're right of course. I agree with IO540 that the best way to be safe is to check with the DPE. I'm not debating what's a good idea or what is good practice - just the question of whether IMC-r training meets the definition of what's needed for the FAA 15hr instrument training minimum.