what next:
On what legal basis if I may ask? JAR is JAR everywhere I thought. We go to the UK every year for our recurrent trainings and neither has any instructor ever signed my logbook nor did any examiner ever want to see a signature.
The countersignature requirement could well be a UK thing, but it only applies to the revalidation of SEP and TMG class ratings, when doing it by experience. I guess what you're coming to the UK to do, is some other rating which is revalidated by test with an examiner, so no need in that case.