‘My,’ she said. ‘What an ugly term. I suppose I should have expected the establishment to try and suck all the joy out of magic. God knows they try so hard with everything else.’

‘What do you call yourself?’ I asked.

‘Oh, I’m a witch, darling,’ she said. ‘Or a sorceress – depends on my mood.’

‘And who trained you?’

Lady Helena smiled.

‘Who do you think trained me?’ she said. ‘My mother, of course. As her mother trained her and hers before her. It all goes back to Queen Caroline, you know.’

Back to the court of Caroline of Ansbach, who was famously brighter than her husband – the future George II. Caroline, who kept company with Walpole and Leibnitz and did medical experiments on condemned prisoners and orphaned children.

‘Early form of vaccination, darling,’ said Helena. ‘And they all lived happily ever after.’

She also had Phillip Boucherett, former protégé of the great Isaac Newton, as a regular guest at court. There he was happy to impart what Nightingale is pleased to call ‘the forms and wisdoms’ of magic to others in her circle – male and female.

‘Of course,’ said Helena, ‘in those days your lot were hardly what you’d call a reputable bunch.’

According to Lady Helena, the Folly at that time had been reduced to a bunch of quacks, grifters and near charlatans meeting at a floating coffee house moored outside Somerset House. The true intellectual heirs of The Second Principia grew out of Caroline’s salons and later those of Elizabeth Montague and her fellow bluestockings.

They called themselves La Société de la Rose – The Society of the Rose.

‘Why was that?’ I asked.

‘I have no idea,’ said Lady Helena.

But this alliance of posh women and pushy middle class entrepreneurs wasn’t going to last. By the end of the century the need for an organised response to all things magical had become obvious to the state – even one as cheerfully laissez-faire and corrupt as the British.

The Scottish led the way, with many from the famed Edinburgh Club arriving in London. And, by the 1760’s, they were calling themselves practitioners, greasing up their patrons and hoovering up the cash.

‘As soon as they got a whiff of respectability they couldn’t dump the women fast enough,’ said Lady Helena. Being a female practitioner became as disreputable as being a female . . . well, anything not connected with maintaining a household. The men moved into their brand new club house on Russell Square and slammed the door in the face of the women following behind.

Actually, I had noticed that the Folly’s lecture hall had a separate ‘Ladies Gallery’ which you reach via a back passage off the east staircase. Presumably it was there so proud mothers, sisters and wives could watch their menfolk demonstrate particularly clever new formae or spells. There was a discreet brass plaque and everything.

I decided not to mention this.