Criminal barristers are threatening strike action if the Government does not drop plans to slash legal aid, a leading QC said.

The Criminal Bar Association (CBA), a union of more than 4,000 lawyers, has unveiled a new campaign poster ahead of protests against the proposed cuts in London today.

Nigel Lithman QC, chairman of the CBA, said the public show of defiance - illustrated by the threat of unprosecuted paedophiles and murderers - could be a precursor to industrial action as early as January 2014.

He said: "If the rally doesn't work, then more drastic action has to be taken. The criminal bar is not prepared to work in the face of these cuts."

Plans for a strike are reportedly due to be discussed at the rally outside Lincoln's Inn today, where lawyers will march against plans to slash £220 million from legal aid.

Justice Secretary Chris Grayling moved to cut a further 30 per cent from the £1 billion-a-year legal aid bill in April despite a 40 per cent reduction in funding since 1997, a decision that Mr Lithman said would cripple criminal trials.

He said: "The most serious cases are collapsing. Barristers are going to court, telling the judge that the Government has changed the terms of their contract. They're not prepared to work on that basis, nor are they prepared to take future cases on that basis.

"This is the most immediate problem the bar and the Government faces; how they manage to arrange representation of those people whose barrister's position has been made untenable by the Government.

"People are not only walking away from the profession, but other people won't come into the profession. Without them it will be impossible to prosecute serious criminals or defend the innocent ones."

According to the CBA, 98 per cent of British barristers are not prepared to work under the proposed changes. It reports that 60 per cent of those now face working for fees of less than £20 a day.

Mr Lithman continued: "People coming to the bar will be facing debts of £72,000 - and scholarships granted by chambers won't be offered because the rates of pay are being driven down. The criminal bar will become closed to people from a working class background.

"In any event, why would people want to come to one part of the legal profession where a commercial counterpart would earn in an hour what they earn in a week.

"The bar is not about a dozen people that have earned handsomely, it is about the 5,000 that makes the court tick and do so with standards of excellence that are disappearing."