I had found the two motorcycle pictures before on one of my many trawls through the internet. I did not know the story behind them though and have found it to be an interesting read.
I don't know if I missed something in the article, but why did he hide all his belongings, including uniform, in the desert? Going on a spy mission, in civilian wear? Or just afraid to be captured in uniform? Questions, questions....
As Sven mentions, it is surprising that no-one has advised the web-site that the bike is a 1940 WD16H from either contract C6653 or the early part of C7353.