Last month, they were ordered to pay pounds 3,000 costs for wrongly imprisoning a 70-year-old woman and a mother of three, but a crucial part of the Access to Justice Bill, which has just reached its report stage, contains a clause granting magistrates immunity for wrongful imprisonment.
Among all the controversy over the bill and its plans to reform legal aid, the removal of the Divisional Court's power to impose cost orders against individual magistrates has escaped the attention of many lawyers.
Every year, around 25 liability orders are imposed against magistrates by the Divisional Court, which rules that they have acted outside their powers. This month, Bristol magistrates were forced to quash decisions after they imprisoned four people - one mentally ill and another with learning difficulties - for non-payment of financial penalties.
Next month, the Doncaster magistrates - perhaps sensing the resolve to fine magistrates is weakening in the face of the Access to Justice Bill - will go back to court in an attempt to have their liability orders overturned.
At the original hearing, Mr Justice Collins said that he felt compelled to impose the order against the magistrates because "there were so many breaches of the appropriate principles [of law]".
Both women had been given custodial sentences which were suspended after they agreed to pay. When they failed to keep up the payments the court ordered them to appear before magistrates, but they did not arrive. The magistrates jailed them in their absence without issuing a warrant ordering them to court to explain their failure to keep up the payments.
Elizabeth Jack, who was on income support and, after hip replacements and a subsequent fall, walked with the help of a Zimmer frame, was sentenced to 90 days for failing to pay pounds 600 poll tax arrears.
The same bench, chaired by Joan Lucas, jailed Alison Christison, 31, a single parent, for 28 days. She was given no time to arrange for the care of her children.
Ian Wise, the barrister who has made a name for himself representing fine-defaulters who have been wrongly imprisoned by magistrates, believes the proposed change in the law would lead to thousands more cases of magistrates wrongly imprisoning the most vulnerable members of society.
"If magistrates cannot be held personally liable to costs orders," Mr Wise said, "then there is no incentive for them to settle. Instead, thousands of cases will proceed to the High Court which otherwise would have settled." Mr Wise said the fear of a costs order forced magistrates to think carefully before they committed people to prison.
One senior clerk at a north of England court said that court clerks had been told unofficially to advise their magistrates to avoid imprisoning single mothers, the disabled and elderly because of the risk of legal challenges.
Bruce Houlder QC, chairman of the Bar Council's public affairs committee, said that under plans drawn up by the Home Secretary Jack Straw, more and more powers were being given to magistrates to try cases. He said they were not trained to the same degree as judges and the opportunity for "innocent error" was therefore much greater.
Barrister Alan Murdie, former chairman of the Poll Tax Legal Group, accused the Lord Chancellor of interfering with the independence of the judiciary by removing a judge's right to impose a costs order against a magistrate.
"If these measures go into law, justices will be able to breach fundamental human rights and disobey the law every week without being in fear of personal consequences," he said.
Mr Wise said he now intended to make representations to the Lord Chancellor in an attempt to get him to reconsider the proposals. He will remind the Lord Chancellor that five years ago 22,500 people a year were committed to prison for non-payment of financial penalties, whereas today the number has fallen to just 6,000 a year.
This, said Mr Wise, had much to do with legal aid being made available to those who wanted to challenge their imprisonment.
A spokesman for the Lord Chancellor's Department said that the immunity clause put magistrates on the same footing as judges, who have always been protected from costs orders.