So steam it was. And because of that the London Underground was a lot less underground than originally planned. Where the tracks ran under an existing roadway they put in steam grates and, wherever the tracks didn’t, they tried to leave the roof off as much as possible. One such ‘cut’ famously existed at Leinster Road where, in order to hide the unsightly railway from sensitive middle-class eyes, two brick facades were built that seamlessly replicated the grand Georgian terrace that had been demolished to dig it. These fake houses, with their convincing but blind painted windows, became an endless source of humour to the kind of people who think making minimum-wage pizza delivery guys go to a false address is the highest form of wit.

Everyone knows about Leinster Road, except perhaps minimum-wage pizza delivery guys, but I’d never heard of any fake houses west of Bayswater Station. Once you knew what you were looking for they were easy to spot on the satellite view of Google Maps, although their nature was somewhat disguised by the oblique angle of the aerial photograph. Me and Lesley talked our way into one of the flats above the shopping arcade on the Moscow Road, which had a good view over the back of the house where Kevin Nolan had delivered his greenery. From there it was obvious that, while the buildings were less than a full house, they were more than just a facade.

‘It’s like someone only built the front rooms,’ said Lesley.

Where the rear rooms and back garden should have been there was a sheer drop to the track bed six metres below.

‘Yes,’ I said. ‘But why?’

Lesley dangled the keys she’d confiscated from Kevin Nolan in front of my face.

‘Why don’t we go find out?’ she said. She must have detached them from Kevin when we put him in a car to send him off to AB to be interviewed.

Both of the houses were part of the same facade but we chose the door that Kevin had used on the basis that he’d known what he was doing.

It looked like an ordinary front door, set deep in the mid-Victorian fashion with a rectangular fanlight set above. Close up I could see that the door had been crudely repainted red without stripping the original paint first. I picked a flake off and found it had been at least three different shades, including an appalling orange colour. There was no doorbell but a tarnished brass knocker in the shape of a lion’s head. We didn’t bother knocking.