5 June 2017 - Machin 50th Anniversary 1st class PIP Machin stamp from PSB
The 1st class PIP definitive was originally issued in 2006, when the pricing of mail was changed to size-and-weight, rather than just weight. There were several printings of this by different printers. This new stamp is from the Anniversary Prestige Stamp Book.
This is not a new stamp in the SG Concise Catalogue level, but may be listed in the Specialised Catalogue.
In the picture, an earlier stamp is on the left, and the 2017 one on the right.