Dear Mary | 31 May 2018

Q. I work at a desk by a window which looks out on to the street where I live. I am disturbed by the sight of the same Englishman strolling past the window innumerable times per day. I know most of my neighbours and he is not one of them. Who is he? I can’t think of a reasonable way to ask him, nor do I wish to encourage a friendship, but this mystery is beginning to obsess me.
— I.D., London W11

A. Put some marketing bumf into an envelope and address it to, for example, ‘John Brown’ with your street name and postcode, but the house number missing. Write ‘By hand’ on the envelope. Next time you see the man, rush out with a pile of post. Announce that an important-looking envelope has been misdelivered to your home and, since you know most of your other neighbours and see him so often but haven’t yet been introduced, you assume it must be for him.