It must be exhausting to be a monarchist, forever finding ways to pretend a family of cold, talentless snobs are better than the rest of us. They have to make gold out of mud. The system of monarchy – selecting a head of state solely because of the womb they passed through, and surrounding them with sycophants from the moment they emerge – produces warped and dim people and demands that we scrape before them. What's a poor monarchist to do? They can only lavish a thick cream of adjectives – "dignity", "charm", "majesty" – over the Windsor family in the hope that some of us are fooled.

This process corrupts even the most intelligent monarchists. A strange case study is the new, authorised, 1,000-plus pages biography of Elizabeth Bowes-Lyon (the "Queen Mother") by William Shawcross. He is a smart man: his study of the secret bombing of Cambodia by Henry Kissinger is extraordinary. Yet as a monarchist he has an impossible task. He has to present a cruel, bigoted snob who fleeced millions from the British taxpayer as a heroine fit to rule over us. His mind turns to mush. Before the real Bowes-Lyon is lost in a frenzy of royalist rimming, we should remember who she really was: more Imelda Marcos than the good fairy Glinda.

By the time she died, Elizabeth Bowes-Lyon was treating the British Treasury – our tax money – as her personal piggy bank, with her bills running way beyond the millions she was allotted every year. Even the ultra-Tory Chancellor Norman Lamont complained that "she far exceeds her Civil List and the Treasury gets very het up about it". She used the money to pay for 83 full-time staff, including four footmen, two pages, three chauffeurs (what do they do, split her into three parts for transportation?), a private secretary, an orderly, a housekeeper, five housemaids... the list goes on and on. She even insisted that it was a legitimate use of public funds to maintain a full-time "Ascot office", whose job was to do nothing but keep a register of members of the Royal Enclosure and send them entry vouchers.

Download the new Independent Premium app Sharing the full story, not just the headlines

She presented this spending (enough to open and run a new hospital that would save thousands of lives every year) as an act of selfless patriotism. Michael Mann, the former Dean of Windsor, who knew her very well, explained: "She feels that Britain is Great Britain and that, therefore, ours must be no banana court. To lower standards [i.e., her spending on champagne, caviar and limos] is to denigrate the country and, insofar as high standards require big spending, so be it." When single mothers take 0.1 percent of this sum from the state, the same newspapers that lauded Elizabeth as "the best of British" savage them as "scroungers". If they refused to pay tax – as Elizabeth did – they would have been put in prison.

What did she do to earn these vast sums? Her parents were "Lord" and "Lady" Strathmore, and from birth she was waited on by a gaggle of servants including a butler, two footmen, five housemaids, a cook and numerous room maids. She grew up with four palaces at her disposal, but it wasn't enough. She was obsessed with "bloodlines", which she believed determined a person's worth, and wanted to marry into what she regarded as "the best" – the Windsor family. At first she tried to woo Edward Windsor, but when he wasn't interested, she settled for his stammering, highly strung younger brother, George. When Edward became King, she plotted to force his abdication so George could ascend and she could become "Queen". His "crime" was to fall in love with a divorcee – and one with such poor bloodlines! Once Edward was successfully toppled, Elizabeth insisted that he and his wife Wallace be driven into exile and blanked by royal circles (the couple had plenty of real flaws, but Elizabeth was blind to them: it was the American-ness and the divorce that she loathed).

This was her way with any relatives who displeased her by showing vulnerability. When her cousins became mentally ill, they were locked in asylums and never seen again. Elizabeth's entry in Who's Who? falsely announced that they were dead.

This icy ruthlessness startled people who met her. In 1939, the French prime minister Edouard Daladier said she was "an excessively ambitious young woman who would be ready to sacrifice every other country in the world so that she might remain Queen".

The most striking aspect to Shawcross's biography is that, once she had contrived to marry, Elizabeth really didn't do anything else for the rest of her life except spend, spend, spend – our money. He has to pad out whole decades. She didn't even raise her own children: she would see them for an hour a day and get them to chant: "We are not supposed to be normal. We are not supposed to be normal." But to be fair, she did do one more thing. In her spare time, she supported far-right politics. She was a passionate defender of appeasing Adolf Hitler, lobbying behind the scenes to garner support for Neville Chamberlain. The reasons are plain: even 50 years later, she bragged to Woodrow Wyatt that she had "reservations about Jews". Once the war began, she was rebranded as a symbol of Britain's heroic resistance to the Nazis, but what did she actually do? Unlike everyone else, she didn't live on rations, but was fattened by pheasants and venison on the royal estates. She didn't stay in bombed-out London very much, anything like as much as the myth suggests: she spent much of the war in Windsor, Norfolk and Scotland, far from the Nazi planes, surrounded by battalions of servants.

Elizabeth Bowes-Lyon kept up her support for far-right politics throughout her life. She did everything she could to bolster the torturing, white minority tyrannies in Rhodesia and South Africa, because – as the journalist Paul Callan, who knew her, put it – "she is not fond of black folk". Our beaming Queen Mum was Alf Garnett in a tiara.

She believed Britain's class system reflected a natural hierarchy, and the people below her creamy, upper tier were inferior. She told Wyatt: "I hate that classlessness. It is so unreal." At first, she was appalled by the idea of her eldest daughter marrying Phillip Mountbatten because his "bloodlines" weren't good enough: his family had fallen from power, so they weren't "really" royal. When Diana Spencer started hugging Aids victims and lepers, Elizabeth was disgusted. When Diana started rebelling, Elizabeth announced to friends that the girl was "schizophrenic", but she was bemused because Diana came from "a good family". The rest of us, by implication, come from "bad families", where you would expect schizophrenia and other lower-class disorders.

The defenders of Elizabeth were left claiming that her drunken inactivity was itself an achievement. WF Deedes, the late Daily Telegraph columnist and editor, claimed: "In an increasingly earnest world, she teaches us all how to have fun, that life should not be all about learning, earning and resting. In a world where we have all become workaholics, there she is... grinning at racehorses. Bless her heart." He was in favour of the dole after all, provided it was worth £3m and went to one single aristocrat.

William Shawcross has won the favour of his fellow monarchists by taking this curdled life and presenting it as the best of British. It's the single most unpatriotic claim I've ever heard. If you don't think Britain can do better – far better – than this nasty leech and her stunted family, then you don't deserve to live in this Sceptred Isle.

j.hari@independent.co.uk