These sort of 'ramp checks' are fairly common, I've had it happen to me twice. Both times with G-reg permit machines and as Rod says, they know what they are looking at and if someine is not in order then the impression is that things will get difficult.
They do seem to concentrate on 'foreign' registered machines - certainly the last time it was only those where the pilots were being located and the paperwork reviewed.
But none of this is about VAT much more the sort of thing that the FAA carry out in the US.
Interestingly on my last trip there seemed to be more N-reg machines which looked to be based in France. I spoke to several pilots who pointed to their Cirri or larger Cessnas - which were N-reg'd