Looks like Auro Transparent Varnish is available in the Uk (No 251 - same one).
At one time I wouldn't even use plastikote! I was concerned about any kind of paint in a hamster cage and preferred to scrub wood clean or replace it - but if it's a large area ...
AURO 251 CLEAR GLOSS LACQUER – Greenshop
Useful if anyone doesn't want to get it sent from Rodipet in Germany maybe!