It was made from a Luger, either a toy or the Japanese model kit that was available at the time (Oh I miss those kits). It has the large front bulge on the grip, and you can see part of the shoulder stock rail at the back. The BBC, like all networks was going to go the cheapest route available, and a toy or model kit fits that bill.
I had a model kit of a Nambu back in the late 70s and the grip was not as large as a Luger's, because the 8mm cartridge is not as long as a 9mm. The 8mm cartridge was considered to be about as powerful as a .32acp round.
David.