Bought these two large repro photos today,they are 17"x12"the seller said they were taken at Bordon camp,they show mainly M20 with a few Triumphs and civilian models.
These photos are all over the net, though not in large format. I doubt that the seller has the copyright, which seems to be the modern business model with wartime photos....
Not sure where I got mine but the cost nothing, probably the same source as yours. I think the real source is a motorcycling magazine of the period.
They are quite well known pictures which we have discussed here before but they are interesting in that they prove some early specification machines made it to the end of the war without modification to later spec.
Presumably this sale was organised by the Ministry of Supply and all the machines with number plates were from other government run departments such as the Civil Defence, NFS, Police ect.