so what does this do for night flight in the UK which is automatically IFR aaaaaarrrrrrggggghhhhhh nooooo not that one again!!!!!
Not a lot.
If the pilot has a JAA night rating then he can fly at night on his JAA license. If he doesnt, he cant. That means if he has an FAA license, piggyback or otherwise, in the UK he will be flying on his JAA license in an N reg, so it makes no difference.
The only case it would be a problem is if he only had a stand alone FAA license without an IR in which case he couldnt fly an N reg at night - unless he asked for a SVFR clearance - in which case he could.