‘Good one, sir,’ I said.

‘No, really,’ said Nightingale, ‘he’s the only person authorised to make the final decision.’

New Scotland Yard was once an ordinary office block that was leased by the Met in the 1960s. Since then the interior of the senior offices had been refitted several times, most recently during the 1990s, easily the worst decade for institutional decor since the 1970s. Which was why, I suppose, the anteroom to the Commissioner’s Office was a bleak wilderness of laminated plywood and moulded polyurethane chairs. Just to put visitors at their ease, photographic portraits of the last six Commissioners stared down from the walls.

Sir Robert Mark (1972–1977) looked particularly disapproving. I doubt he thought I was making a significant contribution.

‘It’s not too late to withdraw your application,’ said Nightingale.

Yes it was, but it didn’t mean I wasn’t wishing it wasn’t. Typically, a constable only sits in the Commissioner’s anteroom when he’s been very brave or very stupid, and I really couldn’t tell which one applied to me.

The Commissioner only made us wait ten minutes before his secretary came and fetched us. His office was large and designed with the same lack of style as the rest of Scotland Yard, only with a layer of fake oak panelling on top. There was a portrait of the Queen on one wall and another of the first Commissioner, Sir Charles Rowan, on the other. I stood as close to parade-ground attention as any London copper can get and nearly flinched when the Commissioner offered me his hand to shake.

‘Constable Grant,’ he said. ‘Your father is Richard Grant, isn’t he? I have some of his records from when he was playing with Tubby Hayes. On vinyl, of course.’

He didn’t wait for me to answer but shook Nightingale’s hand and waved us into our seats. He was another Northerner who’d come up the hard way and done that stint in Northern Ireland which appears to be obligatory for would-be Commissioners of the Metropolitan Police, presumably because violent sectarianism is thought to be character-building. He wore the uniform well and was judged by the rank and file as possibly not being a total muppet – which put him well ahead of some his predecessors.

‘This is an unexpected development, Inspector,’ said the Commissioner. ‘There are some that would see this as an unnecessary step.’

‘Commissioner,’ said Nightingale carefully, ‘I believe circumstances warrant a change in the arrangement.’

‘When I was first briefed about the nature of your section I was led to believe that it merely served a vestigial function, and that the—’ The Commissioner had to force the word out. ‘—that “the magic” was in decline and only posed a marginal threat to the Queen’s peace. In fact, I definitely remember the word “dwindle” being bandied about by the Home Office. “Eclipsed by science and technology”, was another phrase I heard a lot.’