18/04/2012 18:31 BST | Updated 18/06/2012 06:12 BST

The King's Mistress

When she wrote her memoirs of her life as the most powerful courtier at Queen Anne's court, Sarah, Duchess of Marlborough lamented that, "Women signify nothing unless they are the mistress of a prince or a first minister." Sarah may or may not have been Queen Anne's lover. But she had the queen's favour and enjoyed phenomenal power until her spectacular fall from grace, which distressed her so much she smashed the furniture.

With her loss of power Sarah was rendered useless politically. She was right to emphasise her female insignificance in her memoirs; 18th century women only enjoyed power if they had access to powerful men. (Queen Anne, although a woman, behaved just as her predecessor Elizabeth I had done; both ruled in a masculine style, which deviated not at all from the behaviour of their antecedents). But the power a favourite could wield was very real; clever, beautiful and ambitious women could achieve it if they were attractive enough to the men who ruled them, and it often made them rich.

Melusine, Duchess of Kendal and mistress of George I was a woman at the apex of British politics and court life. With George, she successfully presided over the transition from Stuart (Scottish) to Hanoverian (German) monarchy in Britain. She intrigued, she took bribes, she practiced diplomacy, she was courted by the glitterati and she involved the country in breathtaking scandal. Most importantly, very little, if anything, was done by the king's ministers without her say so. Robert Walpole, Britain's charismatic first Prime Minister, said that she was, "As much Queen of England as any ever was." But for a mistress, Melusine was unusual; she was not particularly decorative.

George was uxorious. After he divorced and imprisoned his wife, the volatile Sophia Dorothea of Celle, he committed himself to Melusine. (They met when she arrived in Hanover to take up a post as lady-in-waiting to his mother the Electress Sophia). Melusine was not conventionally beautiful. Contemporary fashion favoured the plump - paradoxically the ideal of physical beauty was Sophia Dorothea - and Melusine was very slim. Her detractors, mostly the Tories and the Jacobite press, were vicious, accusing her of meddling, of avarice, and of sexual depravity; she is the most vilified mistress in British history because, her foreign birth aside, few could understand the king's attraction to her. But George thought of Melusine as his wife, whether or not they married in secret, and she fulfilled all the functions of a queen consort and held enormous sway. She was clever and witty, amusing George for hours with paper cut outs of the new English ministers he deplored, and the pair were devoted to one another. Through her lover, Melusine held power until his death in 1727. No English mistress or queen consort would ever be as powerful again.

Today, monarchy in Britain is very different. The monarch is a figurehead and it is impossible to imagine an influential, rather than merely cosseted, royal mistress undertaking diplomacy on the state's behalf, or directing civil servants. There is no room in the political spectrum for a Melusine or a Sarah, Duchess of Marlborough in the 21st century. But we still retain our fascination with the mistresses and consorts of presidents, princes and kings. We pour over the clothes of the Duchess of Cambridge and Carla Bruni, examine their hairstyles and we comment on their weight. We took sides in the 'feud' between Princess Diana and Camilla Parker Bowles, comparing their physical and other attractions for the Prince of Wales as if we knew them personally, or as if it mattered. They are our painted toys in an age of celebrity and their lives entertain and thrill us, although we do not tend to analyse their significance, because they have none; our interest is mostly held by their gilded lives, their objects. Any power they have is through the public devotion or envy that they inspire. Although huge inequality remains in remuneration and representation of women, the opportunity for power or influence does exist for women who are lucky, rich or determined, where there was none in the 18th century.

Claudia Gold is the author of The King's Mistress: Scandal, Intrigue and the True Story of the Woman Who Stole George I's Heart published by Quercus, April 2012.