"I've got nothing against your right leg. The trouble is, neither do you." The seed for the one-legged Tarzan sketch, one of Peter Cook and Dudley Moore's finest moments, was sown in the mid-18th century. Its progenitor was the "unidexter" impressionist, playwright and man-about-town Samuel Foote (right), who in his day was one of the most beloved theatrical impresarios in London, a friend and rival of David Garrick, and coffee-house companion of Samuel Johnson. Ian Kelly's impressively researched and gripping biography tells the fascinating tale of a man whose unlikely rise to fame and fortune, aided and abetted by personal disaster, was halted by an even less likely entanglement.

Born in 1720 in Truro, Cornwall, Foote was descended from what he described as "some of the most illustrious families in the kingdom". The glimmer of truth in this  his mother's family were indeed nobility  was outweighed by a long-running dispute over her inheritance, a case that ran a century and inspired the Jarndyce v Jarndyce shenanigans in Bleak House. Sent down from Oxford for idleness and "a long course of ill-behaviour" in 1741, the impoverished Foote became a frequent visitor to debtors' prisons over the next few years.

He achieved a modest level of fame by writing one of the first true-crime books published, which dealt with the murder of one of his uncles by another, at sea. He then made his name in a series of pitch-perfect impersonations of the great and the good, which he advertised as "tea parties".

Foote was a prolific writer, and plays such as The Minor and The Orators proved immensely popular. He was the star attraction in these comedies, often dressed in drag, and mocked his friends and enemies alike without mercy.

A serious setback came in 1766, when, as the result of an ill-considered bet, he lost a leg in a riding accident. Foote managed to turn this catastrophe to his advantage, being granted a royal patent for his Hay Market theatre and even writing a series of star parts specifically for one-legged actors.

However, all would be turned upside down in 1776, when he was accused of "sodomitical assault" by his footman (erroneously reported as being named Roger) and took part in two scandalous trials, which were so widely reported that America's declaration of independence was relegated to a sidebar.

Kelly, who is also an actor (he had a leading role in The Pitman Painters), has a keen eye for the intricacies of the Georgian stage, in which Shakespeare's works were frequently "improved" by actor-managers wishing to increase their own parts. He marshals a wide and disparate range of information confidently and entertainingly. The book moves at a terrific pace, but takes time to prime the reader in everything from the inheritance complications of an aristocratic family to exactly how a limb would be amputated.

At its heart is the enigmatic figure of Foote. His unfortunate name would eventually be matched by an equally dismal reputation, his good standing destroyed by his alleged homosexuality and leg amputation alike. Kelly leaves the questions of Foote's guilt and sexuality ambiguous, albeit with strong hints that explain some of Foote's more bizarre actions towards the end of his life. Never exactly likable or sympathetic, the final impression of Foote is that of a man before his time, and one more sinned against than sinning. Besides, it is hard not to have an enduring respect for a man who quipped, when he heard he was accused of the capital crime of buggery, "Sodomite? I'll not stand for it."

There are three kinds of theatrical anecdote. There's the faintly amusing: the one about the handles coming off the French windows just before a cuckolded Martin Jarvis declares: "You're destroying my home!" There's the apocryphal: the one about the audience member who shouts "She's in the attic!" as the Nazis arrive to sniff out Pia Zadora's Anne Frank. And there's the sort from which the names must remain redacted  such as the tale of a present-day theatrical knight who, in his youth, excused his catastrophic lateness by claiming that his mother had died, obliging her to attend decades of first nights in discreet anonymity.

The life of Samuel Foote  Georgian comedian, satirist, impressionist, playwright and pamphleteer  affords a green-room incident that's rather less easy to categorise. It's the story of how Foote got his first big break. (His second came 30 years later, courtesy of a bad-tempered horse belonging to the Duke of York.) It happened backstage at the Theatre Royal, Drury Lane during a 1735 performance of Robert Fabian's farce Trick for Trick. The leading man, Charles Macklin, decided to pick a fight about a peruke with his fellow actor, Thomas Hallam. "You saucy, impertinent rascal," he raged, "I wonder how such a little scoundrel dared take a wig out of my dressing room?" It seems that Macklin intended only to administer an admonitory poke in the eye with his cane. Unfortunately, he skewered Hallam's brain with it. A manslaughter conviction did not enhance Macklin's box-office appeal, so he diversified into coaching younger hopefuls  principal among whom was a spoon-faced, thick-waisted Cornishman named Samuel Foote  whose only prior claim on public attention was the pamphlet he'd written describing how his Uncle Sam had murdered his Uncle John aboard the HMS Ruby, and claimed that the victim had strangled himself.

Only those who have first ensured that their jaw is a safe distance from any hard surface should read Ian Kelly's uproarious account of Foote's career. Kelly's hero left Oxford with debts of £9,000 (add a zero to get today's equivalent) and the distinction of having induced some cows to ring the college alarums by decking the bellropes with hay. He married for money, but not enough money to cover his debts  and went straight from a Truro honeymoon to the Fleet Prison, the only address he and his wife Mary ever shared. He trolled around Covent Garden in beaver-fur, or an orange suit lined with pea-green velvet  though his cross-dressed alter ego, Miss Dorothy Midnight, toast of London's molly-houses, had even more extravagant tastes. His friends  who were many  included the dissipated Delaval family, whose Northumberland mansion contained a guest-bedroom in which the four-poster could surprise its occupants by dropping them into a bath of cold water. His enemies  who were even more populous  included the publisher George Faulkner, who once hired a gang of Irish beggars to hiss Foote from the stage of the Theatre Royal, Dublin. (The actor counterattacked by impersonating his foe so perfectly that the paid mob was reduced to silent confusion.)

Foote's story reads like a life lived in emulation of the bizarre complexities of his plays  in which, typically, an English nobleman might test the moral character of his son while disguised as a Bavarian baron, or a tumescent knight might attempt to ravish a nun in a darkened room, unaware that she is a Capuchin monk in drag. The flow of inspiration, however, tended to run the other way. When Foote lost a libel case against Faulkner in 1748, his response was to transform the ordeal into a play entitled The Trial of Samuel Foote, Esq  in which he played both the accused and the prosecuting counsel. Later, when accused of an offence that carried the death penalty, he immediately processed the scandal into dramatic performance  inaugurating the process that put the disgraced Rector of Stiffkey on stage surrounded by lions, a shirtless Jeffrey Archer on to the boards of the Haymarket and a befuddled Michael Barrymore into the Big Brother hot tub.

There was, inevitably, a fourth-act reversal for Foote  which came in the form of a "mettlesome steed" on which Foote found himself after making an ill-judged boast about his horsemanship at a country-house weekend in Yorkshire. The granite cobbles of Methley Hall were unforgiving: naked bone burst through the leather of his riding boot. He was saved by a skilful amputation, and, amazingly, returned to the stage  from which he was only dislodged by a scandal in which he was accused of attempting to sodomise his footman. Foote, it was alleged, crammed his fingers into Sangster's breeches while the man was adjusting the straps on his master's cork prosthesis. A story got around that the footman's first name was Roger. Disappointingly, it was John.

Kelly  who is an actor as well as the biographer of Casanova and Beau Brummell  handles theatrical rumour and apocrypha with great care. He shows admirable restraint, for instance, in refusing to entertain a story about Foote's last stand  which describes him evading his detractors by disappearing through a trap door in the stage and vanishing into the night.

But there's at least one moment when Kelly's version of events seems to veer from the record, and it's an important one. When laying out the story of Hallam's death  a primal scene in Foote's story  Kelly gives the awful details of the actor's agony. (Squeamish readers may now wish to flip to the crossword.) The cast of Trick for Trick were exhorted to follow the then-standard medical practice of urinating into the wound. A young actor called Thomas Arne  nephew of the composer  was, writes Kelly, the only cast member who proved capable of answering the call, dooming Hallam to make his final exit from Drury Lane, "pissed on by a stripling transvestite". The evidence given at Macklin's trial, however, tells a different story. The court heard that the dying man himself had called out to Arne: "Come here, you bitch, and urine on me!"  but that in the end the victim was forced to endure a watering from his own killer. Just as horrible, but rather more ironic.

Kelly's book takes its first epigraph from Peter Cook's famous sketch "One Leg Too Few", about the one-legged actor who applies for the role of Tarzan. That memory of Dudley Moore's Mr Spigot, pogoing around a theatrical agent's office like Zebedee in a flasher mac, is a sharp reminder that the acting business is largely ungraced by the people to whom Cook refers as "unidexters". There's Tracy Ashton from the US sit-com My Name Is Earl. There's Herbert Marshall, whose loss of a leg in the trenches didn't prevent him from being suave all over Bette Davis and Marlene Dietrich. There's the Edwardian actor-manager John East, who endured an amputation after stepping on a rusty nail while dressed as Uncle Oojah, the cartoon elephant from the Daily Sketch. That's about it. And no anecdote I've heard about them matches the strange, wild and preposterous stories bound within Mr Foote's Other Leg. All unbelievable, and mostly true.

 Matthew Sweet's The West End Front is published by Faber.