I see two different handwritings and implements on there.
The main code is blocky. The U's have square bottoms. They're even written like we might write "LI", as if the writer preferred a fountain point nib and had a habit of avoiding 'pushing' up vertical strokes. By the third line, it looks like his ball point is running dry and he doubles over the lines. He was taught to write the code squarish and blocky -- he writes "27 1525/6" much more naturally.
It looks like he wrote the note at 15:22 and handed it off to someone else who "lib.[erated]" them at 16:25. Probably the Sjt. wrote the plaintext, encrypted it, and handed two copies of the ciphertext to a (lucky) Pigeon Officer to crack open a crate of unused pigeons and drive them well away from the front lines before releasing them. This took about an hour.
Sjt Stott probably wrote "1522" so small to leave room for the Pigeon Officer to write the release time into the same box. (British and their paperwork). But the Royal Pigeon Service Officer didn't want to cram in the letters, so he just underlined "origin" as if to say "this is the correct time of origin of the pigeon I filled out my part of the form right" and wrote above it by hand.
The form was designed for a single user, but on D-Day you had one guy filling out the form and handing it off. The Sjt. may not have had much practice sending messages via pigeon or this particular form much before.
"27 1525/6" sure looks like "signing off at 15:25 on the 6th" (D-Day was June 6, 1944.) What happened in the three minutes between 15:22 and 15:25? Is that the time it took to make a second copy? If so, then why is the time in the message later than the time at the bottom?
Note that the Pigeon Officer knew the IDs of both pigeons before releasing either one of them.
So if the BBC is representing Mr. Young accurately when he "says Sgt Stott would have sent both these birds - with identical messages - at the same time, to make sure the information got through." then I think Mr. Young may be off the mark.
Young and BBC also make the suggestion that "PABLIZ" correpsonds to "Panzer Attack - Blitz". But clearly these are 5-letter groupings so the correct ciphertext is "PABUZ" which doesn't fit nearly so well.
This is a great book to describe the practical use of crypto by agents and troops in the field in WWII: http://www.amazon.com/Between-Silk-Cyanide-Codemakers-1941-1... Leo Marks - Between Silk and Cyanide: A Codemaker's War, 1941-1945
The autobiography of Leo Marks: _Between Silk & Cyanide_[2] was a good (although I suspect quite heavily dramatised & exaggerated) read about the more human elements and flaws of pen & paper crypto used by the allied resistance groups.
[1] http://www.amazon.co.uk/Colossus-secrets-Bletchley-code-brea...
[2] http://www.amazon.com/Between-Silk-Cyanide-Codemakers-1941-1...
https://www.amazon.com.au/Between-Silk-Cyanide-Codemakers-19...
He's the guy who came up with the idea of using silk for codes, as silk won't be felt during pat-downs (paper will be felt). There's lots in the book of trying to work with local business who were obviously not willing to part with their valuable silk.
The book goes much more into details of transmitting these codes, the hassle of bruteforcing when somebody misremembered their code or mistranposed (there was an army of women working 24/7 trying out all possible codes). Highly suggested if the OP piqued your interest!