Hello,
I apologise if I'm teaching my Grandmother to suck eggs.
After surfing for some info, came across this;
"A GB sign is still required when travelling outside the European Union.
A GB sticker is compulsory when driving in Andorra/Switzerland, even on vehicles displaying Euro style plates (circle of 12 stars above the national identifier on blue background)"
And NO, a 5'x3' Union Flag doesn't count!