5 June 2017 - Machin 50th Anniversary 50p grey from prestige book
This gummed stamp with elliptical perforations is a quite different stamp to many of the earlier ones.
This is not a new stamp at SG Concise Catalogue level, but may be recognised in the GB Specialised catalogue.
There has been only one other gravure printing of the 50p with elliptical perforations, and that was by De La Rue. The picture shows the earlier one on the left, and the latest one on the right.