A cute little loophole used by some is that if you are teaching for a CAA RATING...and have nothing to do with teaching towards an FAA rating..the FAA will accept your UK instructor qualifications...even in N reg aircraft flying around the USA.
You cannot, however, authorise ANY solo work by the student...so you MIGHT not be much use to a US school. Having said that, if you were teaching IMC ratings or twin ratings...it wouldn't matter...and if you had all the required UK ratings and wished to teach for IMC ( a UK only qualification, remember) you may be able to qualify for a special skills visa...and be allowed to work there.....if a school (that teaches CAA courses) will 'sponsor' you.
On the other hand, sign up with some company like Comair, Embry-Riddle blah, blah blah and enrol under a student visa (J1, is it?) then you would be alowed to continue working as an FAA certfied instructor for some two years..I think (don't quote me on that...ask the schools).
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LIVE in peace...or REST in it!