TT, that's a very good, measured and reasonable letter. Though the EU was, for the research "community" a convenient way of collaborating, (though, of course, such collaboration should, and I'm sure, does, include nations outside the EU) that should not preclude alternative arrangements. After all, SERN lies across a border between Switzerland and the EU, and the International Space Station could scarcely be more international! But I don't think we want it run by the UN!
Do let us know of any reply you get from your MP.
Very small point: domicile is different to residency. If someone is domiciled here, then residency can't be denied. But I doubt your MP will be so pedantic- your meaning is clear.