1951 Festival of Britain 2s6d to £1, unique set of 4 horizontal marginal Registration blocks of 12 spanning the sheet

Each block with a Printed Registration Certificate on the reverse with manuscript entries, the 2s6d reading:

“THIS sheet (40 set) 2^s/6^d Postage WAS TAKEN IN THE PRESENCE OF THE POST OFFICE CONTROL OFFICER AT THE FACTORY OF Messrs Waterlow and Sons Ltd. at 123, Clifton St. London E.C.2. FOR REGISTRATION OF THE FIRST PRINT OF the 1951 design

(Signed) E. Carr
CHIEF EXECUTIVE OFFICER
5^th March 1951

(Initialled)
INITIALS OF THE CONTROL OFFICER
SUPPLIES DEPARTMENT
STAMP DEPOT”

The other blocks with the same Registration Certificate and date