9 September 2011 FDC of Machin security stamps from Aerial Post anniversary prestige stamp book
There are many claims for the first aerial post flight, but the first authorised United Kingdom Aerial Post took place on Saturday 9 September 1911, from Hendon to Windsor by Gustav Hamel.
Royal Mail issued a miniature sheet and prestige stamp book to commemorate the this anniversary
The definitive stamps have ordinary gum and are without security slits and the 1st class and 76p have an iridescent layer with the codes M11L MPIL, but this is difficult to see especially as it seems to be under
The three stamps are on a Royal Mail Aerial Post FDC with a pictorial Windsor postmark showing the aircraft.
SG U3012, 3015, 3019