OP
I would say that it being a fairly rare example of your country's history and dire need to arm itself is a justification. There were probably less than 6,650 455 Triple locks ever made. That is counting the rare commercial models before the British order, the approx 5802 originally supplied of which yours is one and then the 812 made up later for old stock for a total of 6,614.
Just FYI: the 812 were the first Triple Locks produced, 666 for the British and the rest sold commercially.
Those made from left over parts were produced last, and there are 691 most sold commercially but some did end up in military service.
Post number 1 of this thread.