If you think London's bad for crime now, you should have seen it in Georgian times!

I have several crime writer friends who were policemen or lawyers before they turned their experiences into fiction. But the man responsible for creating Britain's first police force did it the other way round. Henry Fielding was one of the 18th century's most celebrated novelists, author of Tom Jones and many other bestselling books and plays.

But later in life, he became the chief magistrate of Westminster and the founder of the first incarnation of the famed Bow Street Runners - Britain's first roving constables. Fielding is a character in my new novel, The Art of a Lie, in which he investigates the murder of a Piccadilly confectioner - the husband of my main character, Hannah Cole.

And frankly, the London of Henry Fielding and Hannah Cole was a dangerous place. We might worry about crime and lawlessness now, but the capital of the present has nothing on its Georgian predecessor.

A lack of street lighting meant most roads were in total darkness at night. Dingy alleys and courtyards were the haunt of thieves, and dusk became known as "the footpad hour". Sometimes, robbers would block a street at both ends, beat anyone trapped there unconscious, before stealing everything they owned - sometimes even their clothes. Pickpocketing was rife, highwaymen made travel perilous and people were frequently attacked in their own homes - raped, beaten and robbed.

Sometimes gangs of criminals would raid prisons and watch houses, either to break their friends out of jail, or just to kill the local constables and watchmen.

The criminal justice "system" was wholly unfit to deal with this threat, having evolved haphazardly since the middle ages. Magistrates were responsible for the pursuit, arrest and imprisonment of criminals and often their prosecution, too. They selected local citizens by lot to serve as constables, meaning most were both unpaid and unwilling.

Corruption was a huge problem, with many constables taking bribes to look the other way, or running protection schemes. And magistrates were little better. One London justice was described as "very honest" because he took bribes in only a third of his cases! Very few were pro-active in preventing crime, and most prosecutions of criminals were undertaken privately by their victims. All in all, it was a recipe for mayhem. Into this breach stepped Fielding.

Born into a good family in 1707, his father was the nephew of an Earl and his mother the daughter of a high court judge. Fielding was educated at Eton, but his upbringing was both tragic and chaotic. His mother died when he was just 11 years old, whilst his father was a womanising gambler, despised by his mother's family.

Eventually, his grandparents successfully fought his father for custody of the children. Perhaps unsurprisingly, Henry was something of a tearaway in his youth and later become a drinker and womaniser like his father. Forever in need of money, he turned to writing novels and plays and became a prominent satirist of London society. Eventually, he settled down and married, and when his wife died young, he was said to have been so grief-stricken friends feared he would lose his mind. Consolation duly arrived in the form of Mary Daniel, his dead wife's maid.

But when Mary fell pregnant, Fielding shocked his friends and family by marrying her. The unequal nature of this match meant he was no longer welcome in high society, and his detractors delighted in the scandal. Fielding's life was always a battle between duty and desire. For a long time, he had aspired to become a judge like his grandfather, but that path was now blocked because of his marriage.

Not everything in Georgian London was grim. The Art of a Lie is set in a confectionery shop on Piccadilly. Its owner, Hannah Cole, is struggling to run her business in the aftermath of her husband's murder, because many of her suppliers don't like women in trade. Her customers dwindling, she is determined to transform her fortunes, by introducing Londoners to an Italian delicacy named "iced cream".

It might surprise some to know that making ice cream was even possible in an age before electricity and freezers. Ice was available to buy, harvested from frozen lakes in winter, and stored in ice houses.

Hannah tries sitting her bowl of cream in a bath of ice, but by itself, ice is not sufficiently cold to freeze cream. Eventually, she learns from a Professor of Chemistry that she lacks a crucial ingredient: salt. Mix salt with the ice and it causes an endothermic reaction that in turn, causes the cream to freeze.

Once they learned the art of making ice cream, the Georgians didn't look back. They were great innovators and experimented with ice creams flavoured from everything from Parmesan to artichoke, moulding their confections into the shape of candles, lobsters and pineapples.

Instead, he decided to become a magistrate. As chief justice of Westminster, Fielding lived above his courtroom, in a tall, narrow house on Bow Street - so-called because it was shaped like a bow. On his doorstep were the slum rookeries of St Giles and Seven Dials, as well as the brothels and bath houses of Covent Garden. A steady stream of criminals and prostitutes passed through his courtroom, and it was said that Fielding did not take a penny in bribes. He also carried on writing, and in 1749, he published his most famous novel, Tom Jones.

Soon, Fielding was lobbying his political masters for change. As a model for his reforms, he recruited six experienced and honest constables, who were motivated by a genuine desire to combat crime. They were formed into a mobile squad under a man named Saunders Welch, a local grocer and the High Constable of Holborn.

This squad was the first incarnation of the force later known as the Bow Street Runners, who became famous across the world for their work tackling crime. For the first time, London's villains were confronted by an active opposition, and the Runners quickly acquired a formidable reputation. In 1751, Fielding published his Inquiry into the Causes of the Late Increase of Robbers, which proposed many changes to the criminal justice system.

Yet he encountered a great deal of opposition. Many were worried that the government would abuse these new powers and lock up its critics.

Fielding's mobile squad was also likened to the French police, who patrolled Paris in uniform and were considered a despotic enemy of liberty. To Fielding's great regret, the bill he drafted to enact his reforms never became law, though he did manage to secure more funding for his squad. One of Fielding's preoccupations was con men and fraudsters, the "sharpers" of the 18th-century underworld.

At a time when a man's credentials were hard to verify, a great deal rested upon how he dressed, spoke, acted and behaved. Romantic cons were rife, fraudulent investment schemes entrapped the unwary, wooden nutmegs and quack remedies were sold in the Covent Garden Market.

Today, many of us have received emails purporting to come from an imprisoned Nigerian prince with a fortune only we can help him claim. You might be amused to learn that the scam is at least as old as the Tudor period, when it was known as the "Spanish Prisoner". By the 18th century, the prisoner was a Hapsburg count, and the scam will doubtless keep evolving for years to come. The fascinating world of the Georgian con trick is explored in The Art of a Lie, and I had enormous fun researching the topic.

After years of ill health exacerbated by drinking, Fielding died in Lisbon in 1754. Yet the name "Fielding" would continue to be associated with Bow Street, for his blind half-brother, John, succeeded him as Westminster magistrate.

The "Blind Beak of Bow Street", as John became known, was said to be able to recognise a thousand criminals in London by their voices alone. John Fielding secured more government funding and started the first criminal database. The squad of Bow Street Runners was enlarged, with a mounted division later added. Active in London until 1839, they were then subsumed into the new Metropolitan Police Force.

Many of Fielding's other proposals for reform were eventually adopted, including our present system of prosecution, in which the majority of criminal cases are brought forward and paid for by the Crown. For more on this area of history, I recommend A House in Bow Street by Anthony Babington. Or you could read my novel and see Henry Fielding in action, as he attempts to outwit two characters even more cunning and determined than himself.

• The Art of a Lie by Laura Shepherd-Robinson (Pan Macmillan, £18.99) is published on July 10. Laura will teach a historical fiction writing class at the Theakston Old Peculier Crime Writing Festival this month. Visit harrogateinternationalfestivals.com for tickets and information