Poverty-stricken people are being encouraged to plead guilty to crimes they did not commit out of fear they will face crippling costs imposed by new financial penalties, leading lawyers, magistrates and campaigners have warned.

Legal experts have called for an urgent review of the criminal courts charge, which has been compared to “18th-century” forms of justice after being implemented earlier this year.

The new levy was introduced by the former Justice Secretary, Chris Grayling, to make criminals pay for the upkeep of the courts. Because the charge can be up to 10 times higher if someone is found guilty after pleading innocence, critics say it is undermining the justice system by encouraging impoverished defendants to plead guilty even if they have done nothing wrong.

The charge is not means-tested or adjusted according to the seriousness of the crime. In the magistrates’ court it is fixed at £150 if someone pleads guilty, but it can rise to £1,000 if they are found guilty. Campaigners also say it has created an extra hardship for those whose crimes are motivated by poverty – and makes the punishment for small crimes disproportionate.

Many of those affected are homeless or unemployed, with no hope of paying. Recently subjected to the charge were a man who stole three bottles of baby milk, a woman who pinched a £2.39 bottle of shampoo and a homeless man who took a 99p can of Red Bull.

The Independent has learnt of a case this week where a man from Portsmouth was made to pay the £150 charge – as well as a £250 fine and a £25 victim surcharge – after pleading guilty to stealing a £1 bag of chocolate buttons from WHSmith. The charge was levied just a month after his application for bankruptcy was accepted.

The new policy was introduced on 13 April but since the charge can only be imposed on those whose crimes were committed after that date, the courts are only just beginning to see the full effect. At least 30 magistrates – many of them among the most experienced – have already stepped down from the bench over the changes and many more are predicted to resign as further cases come through.

Richard Monkhouse, chairman of the Magistrates’ Association, the independent charity representing the majority of magistrates in England and Wales, said: “The chief concern of our members is the observation that pleas are being influenced by the charge. Defendants may be pleading guilty in order to avoid a larger financial penalty… We hope that the Lord Chancellor will grant the urgent review we’re calling for and grant magistrates discretion in applying the charge.”

Mr Monkhouse added: “We are seeing experienced magistrates resigning from the bench, and we expect this figure to increase as the cycle of trials with the charge kicks in.”

Cuts to legal aid mean more people are representing themselves, making them less confident of successfully proving their innocence – and more likely to plead guilty in order to avoid exorbitant costs. The charge is so immovable that even if you go to prison for failure to pay it is not wiped out. The debt collection will be outsourced to private firms.

Frances Crook, chief executive of the Howard League for Penal Reform, said: “There’s beginning to be evidence that people who are innocent and would like to say they’re innocent are worried that if they do it will be like Russian roulette. This is encouraging them to plead guilty because it carries less financial risk.

“My concern is that this is starting to illustrate the 18th-century justice we’ve got. If you look at the cases coming through across the country it makes you wonder why we are clogging the courts up with them in the first place.

“There are people paying the charge who are up for domestic violence – that’s fair enough. But then we’ve got someone there for stealing a chocolate bar. It’s shocking that these trivial cases are coming to court at all. This court charge has highlighted a real problem at the heart of the justice system. Many of these people are just hungry.”

Ms Crook compared the charge to the poll tax. “Because it’s mandatory and because it’s a fixed amount it’s a bit like the poll tax. There’s no discretion, which makes it unfair on the people who haven’t got money – as well as those who could pay more. The fines system has always worked on the basis of whether people could pay.”

Philip Keen resigned from the bench on 2 July after serving as a magistrate for 30 years in the Isle of Wight. He said: “I couldn’t justify sitting there and imposing that. Our discretion has been taken away and it goes against everything we’ve been taught about fining people within their means and ability to pay.

“The people we’re dealing with don’t have any money, that’s what [the Government] can’t understand... This charge needs to be knocked on the head quickly because it’s just unfair.”

Bob Hutchinson, who resigned as deputy bench chairman of Fylde Coast magistrates this summer after serving for 11 years, has been an outspoken critic of the new charge. “There’s a strong possibility that people will feel financial pressure to plead guilty when they’re not,” he said.

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Earlier this week District Judge James Henderson expressed exasperation at the charge. Sentencing a homeless man for burglary at Wimbledon magistrates’ court, the judge told the court of his disappointment that he was unable to waive the charge because he had no discretion to do so.

A Ministry of Justice spokeswoman said: “It is right that convicted adult offenders who use our criminal courts should pay towards the cost of running them. The introduction of this charge makes it possible to recover some of the costs of the criminal courts from these offenders, therefore reducing the burden on taxpayers.”

Charging for justice

Louise Sewell, 32, was forced to pay the Criminal Courts Charge after pleading guilty to stealing a four-pack of Mars bars worth 75p in the wake of a benefits sanction. She stole the chocolates from a Kidderminster shop on 22 June because she had no money and had not eaten for two days. A campaign to help her has already raised more than £15,000.

Janis Butans, 34, from Derby, stole three bottles of baby milk from Sainsbury’s on 18 July. As well as the £150 Criminal Courts Charge, he was handed a six-week community order with curfew and was ordered to pay £85 costs and a £60 victim surcharge.