Having been searching for something else with no luck whatsoever, I idly popped that reference into Google, and found this. Of course, that’s not a guarantee that it’s correct…
http://www.ebay.co.uk/itm/BRITISH-ARMY-SEAT-BACK-UNUSED-RADIO-TRUCK-WW11-/161202004505

Thanks chap – actually that is the item, and by the looks of it – my mate has tried to flog one on ebay!! He didnt tell me that! 🙂

Bit of a mystery then really….

TT