Sorry I was only passing through the room when I saw it - not even sure it was Regimental admissions now - will have to look at the programme again on rewind to find out exactly.
When I needed some military records looked up at the NA sometime ago I used a military researcher at very reasonable cost - not sure if he still does it. Kevin Asplin was his name.
Update it was the Honorable Artillery Company that had the admissions book.
It might be worth contacting the Regiment Peter first joined to see what Regimental records they know of that might shed some light. Here's a link to the Regimental Museum.
http://www.doncaster.gov.uk/sections...ry_Museum.aspx
http://www.nam.ac.uk/research/famous...light-infantry