Keith,
If the Swiss bicycle appeals to your son, see
http://www.radfahrer.ch/English/tax/o-rad05.php for some background info.
Another option is to find a BSA Mark V or V* bicycle, should be possible to find one in Britain? Read
http://oldbike.wordpress.com/1939-19...k-v-army-bike/ for more info.
Military bicycles are more interesting than meets the eye. I have a Dutch military bicycle, and I think you will find it is harder to find parts and spares for a military bicycle than it is for CMPs. . .
Here´s hoping you find a nice example!
Regards,
Hanno