Bookworm - you are presumably bothered by the requirement under FAR 61.3(e)(1) which obligates a pilot to hold (inter alia) an instrument rating in order to be able to fly under IFR, regardless of the met. conditions.
This used to bother me too until I spent an evening recently with one of the FAA's legal counsels. He pointed me to the word "appropriate" in that particular regulation.
His guidance was this. That if the pilot is operating the aircraft in accordance with a licence issued by a foreign country, and if he is operating the aircraft in that country in accordance with the privileges of that foreign issued licence, the the "appropriateness" clause of 61.3.(e)(1) was deemed to be met.
The same would apply to a pilot flying an N-reg in cloud in the UK on the strength of a UK IMC rating - all other aspects of his UK-issued licence being valid and appropriate.
You are obviously entitled to value this advice as you see fit.
2D