The things one finds in the archives of one's national intelligence services, in this case, Britain's MI5.

Here are some excerpts from the BBC story:

... the guide emerged when the Germans initially seized papers from Soviet agents during the war. When the Germans were themselves in retreat, the guide somehow fell into the hands of MI5.

The guide, a kind of Time Out of its era without the shopping recommendations, lists what to do in London, including the best places to meet without blowing your cover.

Hotels were considered to be tricky places in which to operate.

Some such as the Dorchester and Ritz required the "necessary social standing". Others could consider you suspicious if you acted differently.

"It is advisable to arrive at all hotels with smart and sufficient luggage. The British spend a lot of money on good luggage and travellers risk being turned away or asked for a deposit if they do not comply with this custom," says the author.

As to the author, it is suspected to be Leopold Trepper, a Polish Jew recruited by the Russians after the Second World War broke out. He was captured by the Germans, survived that, but barely survived Stalin's paranoia.

He eventually returned to Poland and retired in Israel.