Success. The record was for the correct person, and the wrong year of birth (1894 instead of 1897 as on his birth cert) stated on all the documents, so it wasn't a typo. I can't see any reason for him to have lied about his year of birth. He would have been old enough to enlist in WW1 so would not have needed to lie then. In WW2 perhaps it was better to be older, to avoid seeing action?
The attestation showed him signed up for 4 years service in the Territorial Army Reserve (National Defence Company) in June 1939. He declared being in the 1st Cambridgeshire Regt in 1914, and in the Royal Engineers in 1919.
The file of papers included his service record and various loose documents, from which I've summarised:
1940 posted to 9th Suffolk Regt
1941 June - letter from Cambridge police saying he appears to be a suitable person for the blue caps
Jun 1941 transferred to the Corps of Military Police, Bournemouth. VP [=vulnerable points wing]
Sep. Posted Eastern Command. Depot. Auth. APM/VP 5/41 + Coast/Adm/B/VP/146
May 1942 posted to 302 Company (VP)
Oct 1942 Posted to Y list
Dec 1942 Posted to 302 Company (VP)
Feb 1943 Signed official secrets act
June 1943 303 Company (VP)
April 1944 304 Company (VP)
June 1944 303 Company (VP)
14 Jan 1945 395 Company (VP)
23 Jan 1945 303 Company (VP)
Feb 1945 416 Company (VP)
May 1945 375 Company (VP)
July 45 Y List
Sep 45 Discharged as permanently unfit for any form of military service. ex 375 Company VP CMP
Noted that 'disability under 20% Unconnected E.5.'
If anyone has insights on the above abbreviations, that would be useful. eg unconnected E.5.
Were any of these companies posted overseas? Are there any accounts of where these companies operated?
Bournemouth cropped up a few times - seems to be the location of admin for CMP personnel.
It appears he was not part of the special ops wing of CMP (as speculated by his family), so that's one question answered.