The Prime Minister is facing embarrassment over plans to scrap the majority of jury trials after it was attacked by the barristers' chambers he helped found.
Doughty Street Chambers, where Keir Starmer worked for more than 15 years, said the proposal to let judges decide all but the most serious cases such as rape and murder was 'wrong in principle'.
And the leading human rights set claimed there was 'no evidence' that cutting back on criminal trials heard by jurors would help tackle the backlog of Crown Court cases.
Its intervention will put more pressure on beleaguered Justice Secretary David Lammy, who is expected to tell MPs this week that victims will be denied justice without radical reforms to the system.
Doughty Street Chambers, whose current roster of barristers includes Amal Clooney, said in a statement: 'Trial by jury is a deeply entrenched constitutional principle and anchors our liberal democracy... We are firmly opposed to the proposals to remove trial by jury for all but the most serious of crimes.
'These proposals are wrong in principle, and there is no evidence that they will resolve the current backlog. Anyone who works within the criminal justice system will know that the problems have been caused by chronic underfunding over a number of years.'
Last night the Tories said the intervention was an embarrassment for Sir Keir, who helped set up Doughty Street in 1990 and was appointed Joint Head of Chambers in 2007 before becoming Director of Public Prosecutions the following year.
Shadow Justice Secretary Robert Jenrick told the Daily Mail: 'This is the latest embarrassment for the Prime Minister.'
'The right to be tried by our peers has existed for more than 800 years - it is not to be casually discarded when the spreadsheets turn red. Keir Starmer and David Lammy once knew this - but now they're in charge they have sold out their principles.
'Labour would rather strip you of your rights than strip the state of its waste and fund the courts to sit around the clock. It's yet more evidence that this Government is not on the side of the British people.'
In another illustration of the widespread opposition to the plan, a Labour MP described it as 'utterly ridiculous'.
In a social media post directed at Mr Lammy, backbencher Karl Turner wrote: 'Doing away with jury trials will make little difference to the backlog but it will make a world of difference to our democracy and our justice system. This utterly ridiculous idea needs putting in the bin fast.'
Even sitting judges have joined in the backlash. The Sunday Times told how two judges at Isleworth Crown Court made pointed comments to jurors last week about the importance of the jury trial system.
The Justice Secretary is expected to tell the Commons tomorrow that thousands of victims are waiting years for justice because of the record backlog of almost 80,000 cases.
He will propose that only offences likely to lead to jail terms of more than five years, such as murder, rape or terrorism, should go before jurors.
It goes further than the recommendation in a review by retired senior judge Sir Brian Leveson, who said offences with sentences of less than three years should not be heard by juries.