Between 1840 and 1882, there were eight attempts on the life of Queen Victoria. Apart from the maniacal Hyde Park dandy Robert Pate, who struck the queen on the head with his cane, none came close to succeeding: one would-be assassin dropped his pistol, another got no further than waving his firearm threateningly in the direction of the royal carriage and yet another was beaten to the ground by two passing Etonians wielding umbrellas. Although the charge for threatening the life of the monarch was high treason, for which the punishment was to be hung, drawn and quartered, all the lost and melancholy rag-bag crew of men at the centre of Paul Thomas Murphy's gripping book were sentenced either to the lunatic asylum or to transportation with hard labour.

Unravelling a rich skein of themes  justice, monarchy, prison, policing, public fears and private lunacy among them  Murphy shows how the survival of Victoria was also the survival of the British monarchy. As the queen observed: "It is worth being shot at to see how much one is loved." Inheriting in 1837 a throne whose recent incumbents had been for the most part foreign, degenerate and unpopular, the courage of Victoria (and Prince Albert) in the face of these assassination attempts earned admiration at a time of political and social unrest. The queen refused to cower from the crowd and consolidated her popularity by insisting on walking freely among her subjects.

All the eight men here showed degrees of mania but Murphy uses them to examine larger public fears. The press looked for conspiracy theories: the right feared a politicised working-class, as represented by the Chartists, and the left the threat from Hanover  Victoria's reactionary uncle King Ernest was thought to be plotting domination.

The largest subject in the book, however, is madness and its definitions. The most obviously deranged of the eight was Roderick McLean who was provoked into a murderous frenzy by any encounter with the colour blue, but it is the first of the assassins, Edward Oxford, whose case exemplifies the parameters of sanity if you live in a world marked by inescapable poverty and hopelessness. It was a fantasy of notoriety that made Oxford buy a pair of duelling pistols and take a pot shot at Victoria in 1840. When his lodgings were raided, police discovered a stash of letters addressed to "Captain Oxford", apparently the leader of a group called Young England. For a while rumours flew that the initials E.R. reportedly engraved on Oxford's pistols stood for Ernestus Rex though it soon transpired that Young England was the creation of a lonely fantasist. Oxford, delighted by the publicity, pleaded insanity: the court heard about his cackling laughter, long silences and torrents of weeping. The plea was upheld and he was incarcerated in Bedlam  a sentence considered too lenient by many (reports of Oxford's comfortable life and daily pint of wine inspired the second shooter John Francis who hoped that he too might be committed to the madhouse). Oxford's period in the asylum was astonishingly productive: by the time of his release, 25 years later, he was fluent in French, German and Italian, wrote poetry, painted and had learned to be an expert wood-grainer and marbler. Oxford emigrated to Australia where he became vice-president of the Melbourne Self-Improvement Society.

Shooting Victoria is a teeming, discursive pleasure. Murphy's book is a feat of historical sympathy, shining light on the larger picture of the 19th century and its indestructible queen.

In this his first book, Paul Thomas Murphy, an American enthusiast for Victoriana, recounts seven attacks  few of them attempted assassinations  on Queen Victoria, and argues that they had consequences that previous historians have underrated. They changed both law and policing, he believes, but most of all, they demonstrated the heroism and political sapience of the Queen. "Victoria, with unerring instinct and great gutsiness, converted each episode of near-tragedy into one of triumphant renewal for her monarchy," he declares. The seven assailants intensified "the great love story between Victoria and the Victorians".

Murphy's eagerness is at times endearing. But there are problems with his thesis. For instance, the M'Naghten Rules of 1843, on the criminal responsibility of the insane, arose from the case of a schizophrenic who shot a man whom he mistook for prime minister Robert Peel. They had only indirect connections to the assaults on Victoria.

It is true that these attacks excited outpourings from her loyal subjects. "It is worth being shot at to see how much one is loved," the Queen said after an attempt outside Windsor railway station in 1882. But Murphy's big notion that Victoria, "a canny politician", triumphed over her attackers by manipulating popular sympathies, revived admiration of the royal family and thereby created "the stable, modern monarchy that endures to this day" is flimsy stuff. The truth is that she was selfish, stubborn and obtuse in her attitudes to her subjects; her popularity was resuscitated by artful courtiers stage-managing her jubilee years; and it was the court of King George V that settled the monarchical parameters that exist today.

Murphy is nevertheless the first historian to consolidate accounts of all seven attackers. They were deranged individuals without rational purposes  unlike the nihilists, anarchists and nationalists who exploded, shot, stabbed and defenestrated the crowned heads of mainland Europe. He does not satisfactorily explain why England excited unbalanced attackers rather than efficient, politically motivated regicides.

The earliest attacker was a barman named Edward Oxford, who was notorious for falling into trances or bursting into maniacal laughter. He fired two shots at the pregnant young monarch in 1840. After a quarter of a century in Broadmoor, he was banished to Australia. Similarly John Francis, who fired a flintlock at the royal carriage in 1842, was also removed to a penal colony in Australia, where he eventually prospered.

The botched attack by John Bean, a hunchbacked dwarf who brandished a pistol at the royal carriage, led to a rough weekend for Londoners with spinal deformities. After Bean's description was circulated, innocent hunchbacks were detained in what Murphy calls "one of the most ludicrous episodes in the history of police profiling". Once apprehended, Bean was charged with common assault, and sentenced to 18 months' hard labour. He later committed bigamy, and took poison in 1882.

In 1849 the semi-destitute William Hamilton  wishing to create an annoyance so that he would be housed and fed in prison  launched the fourth attack on the Queen with a rusty miniature pistol, which was probably unloaded. By contrast, Robert Pate was a Piccadilly dandy notorious as an agitated maniac grimacing at passers-by. He suffered from persecution mania and what we would now term obsessive compulsive disorder. In 1850 he was sentenced to seven years, including transportation to Australia, after hitting the Queen with his walking-stick.

Arthur O'Connor, a teenager gripped by grandiose genealogical fantasies, ran at Victoria with an unloaded, broken pistol in 1872. He was eventually confined in an Australian asylum, where he suffered paranoid delusions  once refusing to drink liquids for fear of drowning the Virgin Mary inside him. Doctors attributed his madness to masturbation.

The final attacker, Roderick Maclean, was schizophrenic: he believed that God had revealed to him the secrets of universal power, which lay in the number four and the colour blue. He tried to derail trains, tramped around England carrying a dagger, and was committed to an asylum after threatening to kill anyone in Weston-super-Mare who wore blue clothes. After this bedraggled figure shot at the Queen, he was confined in Broadmoor for the remaining 39 years of his life.

Victoria wanted all those convicted of physical attacks on the royal family to be banished to Australia. "Her safety and peace of mind will be in constant danger," she complained to Gladstone, "thereby making it almost impossible for her to go about in public  or at all in London, if she has no security that such miscreants will NOT  alarm & insult her again". At a time when we are encouraged to respect contemporary victims' voices, it seems harsh of Murphy to describe the sovereign's protests about the sentences on her assailants as "imperious, Queen-of-Hearts rage".

Although Murphy revels in Victorian criminal trials and popular outcries, his skimpy knowledge of the administration and influence of the royal court hobbles his book. It is symptomatic that he keeps calling aristocrats by the wrong titles  the Dowager Duchess of Roxburghe is misnamed, Lord Londesborough is called Jonesborough  and further muddles them in a havoc-strewn index.

He thanks his wife, Tory Tuttle, for patiently tolerating "my freeform articulations of the undigested results of my research". Unfortunately, the freeform articulations are still evident. Murphy is a discursive, if not rambling, narrator who includes an abundance of extraneous material, which some readers may find colourful, but others will consider exasperating or pointless. His prolonged courtroom reconstructions explain surprisingly little. The book is twice as long as it need be  and none the better for its cheerful verbosity.

 An English Affair by Richard Davenport-Hines is published by HarperPress.