5 June 2017 - Machin 50th Anniversary 20p Double-head stamp from PSB
This 20p Penny Black anniversary with elliptical perforations stamp is included in a pane in the Anniversary Prestige Stamp Book.
This is a new stamp and has been allocated number 2331 by Stanley Gibbons catalogue editors, who have changed the existing similar 1st class black stamp from 2331 to 2331a.
A similar stamp with ordinary perforations is in the Golden Anniversary miniature sheet. This is a new version of SG 1470.