There was an article about it in the FWC magazine several years ago (might even have been back in the days of the National Federation of Master Window and General Cleaners)
I attended a NFW&GC exhibition in London when Scot Young gave his address regarding this, so got it direct from the horses mouth
He described it as: "We're in a war here, they've got bows and arrows and I've got a machine gun but they can't see my weapon is better than theirs" then went on to describe how he hired the taxi etc. This was in the mid 90's - Scot was an old man by then and made a point of telling us that when people asked him what he did he always said he was a window cleaner, even though by that time his company was a multi-national and he himself a millionaire.
As he was himself the 'Phantom Window Cleaner' I've no reason to doubt the truth of the story. As he told it he only drove around London. I'm sure this way pre-dated Unger, when I started the only squeegees available were Ettore.