The most militant now argued that marriage was as exploitative as prostitution – just another way of purchasing women. Some saw all sexual relations with men as abhorrent. Women like the veteran feminist Elizabeth Wolstenholme Elmy believed that male sexuality was an expression of the bestial side of human nature, and that to indulge it threatened the very existence of society.

Indeed, she considered that nearly all “diseases of woman” – including, bizarrely, menstruation – were due “to one form or other of masculine excess or abuse”.

This man-hating agenda encouraged a move towards sexual separatism, with many campaigners turning their backs on marriage and remaining defiantly single. At the time, they were simply called spinsters; in many cases, we would now consider them to have been lesbians.

In an atmosphere of growing fundamentalism, the hardliners were in the mood for open revolt. All that was needed was a suitably reckless and fanatical leader to show the way.

This is where Emmeline Pankhurst came in. She and her equally formidable daughter, Christabel, would take the sex war to a new level.

Raised in Manchester but educated in Paris, Emmeline was strikingly beautiful, yet her ambition and ruthlessness were evident from the start.

“She should have been a lad,” said her father. He meant it as a compliment, but she heard him “with rebellion in her heart”.

Ironically, she inherited the cause of women’s liberation from her husband, Richard Pankhurst, a failed politician who in 1870 had drafted the first women’s suffrage bill to be put before Parliament. After his death, she set up her own movement called the Women’s Social and Political Union. Such was her personal magnetism that disciples flocked to her like bees to honey. In time, hero-worshipping crowds would throw jewels and watches at her feet.

Her daughter Christabel was even more charismatic and became the pin-up of the suffragette cause. Slender, graceful, and with “the flawless colouring of a briar rose”, she was physically enchanting to men and women alike.

But like her mother, Christabel was utterly ruthless. “In spite of her charm and feminine attraction,” wrote one admirer, “there was in her soul a core as hard and brilliant as steel, and I sometimes thought as pitiless.”

It was Christabel who established the suffragettes’ strategy of deliberately courting martyrdom to win the propaganda war. In 1905, after disrupting a political meeting, she and a colleague spat at a policeman and refused to pay the fine, ensuring they were sent to jail.

She and Emmeline then encouraged their supporters to follow suit, and milked every drop of publicity when they were punished.

Some of the protests were little more than stunts. Burning rags were stuffed into letterboxes, keyholes blocked with lead, chairs flung into the Serpentine, flower beds damaged, and envelopes containing red pepper and snuff sent to every Cabinet minister.

But as we have already seen, there was also real violence – with repeated attempts to assault the Prime Minister, Herbert Asquith. Amid police reports of suffragettes practising with revolvers, there were even fears he might be assassinated. On one occasion, his car was forced to slow down to avoid a woman lying in the road. Other women promptly jumped out and belaboured him over the head with dog whips, his head protected only by his top hat.

Many of the suffragettes jailed for such attacks won further celebrity by going on hunger strike. The Government introduced force-feeding, inserting tubes through their noses and down their throats while warders held them down.