This got pretty complicated. You can see examples of "varnish ink" by searching Google for that exact term, along with the words "great, britain, stamp."
Here is one listed on
ebay:
http://www.ebay.com/itm/1924-1-1-2d...0#vi-contentNow comes the surprise, no such stamp is listed in the Gibbons "4 Kings" so this item must be extremely specialized.
As you can see, the
ebay example looks like it's printed in heavy, sticky, glossy ink, quite different from a normal copy. This is a new one on me. I get the uneasy feeling one could be manufactured with the right solvents and chemicals.
And of course you are right, no comparison to the varnish bars on early Austrian stamps.