I looked over at Nightingale, who looked quizzically back, and decided to explain the implications later. Surprisingly, when I did, his reaction was outrage that somebody had to apply to a panel to determine what gender they were – he didn’t say it, but I got the strong impression that he felt such panels were intrinsically un-British. Like eugenics legislation, banning the burka and air conditioning.

I thought of the little girl in the blue dress – you can’t get a certificate until you’re 18 – it must have felt like a long wait.

Her mother, when I met her, didn’t strike me as someone who liked to wait.

In the black and white world of the David Bailey photographs, Lady Helena seemed taller than she was in real life. In the photos she’d had a pixie bob haircut that had emphasised the smooth oval of her face, and her large eyes with their drag queen lashes. Now her face was in colour, with the wrinkly brown chamois leather complexion that white people get if they spend their lives under a hot sun. The bob was longer, shaggier and streaked with grey.

‘You’ve seen my glamour pics haven’t you?’ she said before I could introduce myself. ‘I can always tell.’

She stood up to greet me and held out a hand. It was slender but her palms were rough and her grip was strong.

She sighed. ‘What a difference a lifetime makes, eh?’

We sank down onto the chairs which, this being the ABE suite, were low-slung 1970’s wooden frame things with square foam cushions zipped into hard wearing pastel covers. Very useful if you have to crash somewhere over night – although you generally have to beat the CID nightshift to them first.

‘Where’s my daughter?’ she asked as soon as I’d finished the caution plus two.

I explained that Caroline was along the corridor being interviewed about her role in this morning’s Harrods incident. I prefixed it with the word ‘serious’, which usually gets a reaction, but Helena seemed a bit too sanguine for my taste. Generally when you’re interviewing somebody and they seem remarkably calm about one crime, it’s because they’re relieved you haven’t found out about something else. You hope this is going to turn out to be some major case-breaking bit of information but, people being people, it’s often the most mundane shit – affairs, porn stashes, secret second families, that sort of thing.

‘What is she supposed to be responsible for?’

‘Assault,’ I said, ‘assault on a police officer, criminal damage, obstruction, assisting an offender and wasting police time.’

Lady Helena gave me a long look.

‘Assault?’ she asked. ‘Did she physically assault someone?’

You see, even the clever ones can’t resist being clever and the next move, if you want them to stay being clever, is to play dumb.

‘In a manner of speaking,’ I said.