The government’s sentencing policy has been described as a “total mess” after David Cameron ordered a u-turn on plans to halve jail time for serious criminals who plead guilty.

In the latest of a series of interventions by the Prime Minister, he ordered  Kenneth Clarke, the Justice Secretary, to abandon his much criticised plan to allow a 50 per cent reduction in sentences in return for guilty pleas.

It’s a move that threatens to throw the Justice Department’s budget into chaos, as shorter sentences are crucial for meeting the demands of a tough spending round, which saw Clarke agree to make 40 per cent cuts.

Clarke was reported to be unhappy about Cameron’s decision, which has left the Prime Minister open to being accused of micromanaging his Cabinet, after earlier this week ordering Andrew Lansley, the Health Secretary to amend his NHS reforms.

In the Commons, Ed Miliband, the Labour leader, said of Cameron: “He is completely shameless and he will say anything.”

Miliband continued, “We read in the newspapers today that the Prime Minister has torn up the Justice Secretary’s proposals because he felt he had to step in and, frankly, I can see why.

“Because there is widespread public concern around this country about this proposal to cut by 50 per cent the sentencing for those who plead guilty.”

Cameron was “in a total mess on his sentencing policy just like on all his other crime policies,” he added.

The prime minister hit back, saying that Labour’s Sadiq Khan, the shadow justice secretary, had also backed the 50 per cent reduction plan.

In an attempt to shore up Clarke, amid suggestions that Downing Street is unhappy with his performance, the Prime Minister added: “He is doing a superb job and there is plenty more fuel in the tank.”

No 10 also backed Khan, insisting that the sentencing reduction plan had never been formally approved by the Cabinet – even though Mr Clarke told the Commons last month it was an “agreed policy.”

It was contained in a “green paper,” which was then put out to consultation, and the Government will give its formal response shortly.

A No 10 spokesman said: “We set out some proposals in the green paper. We listened to what people have to say and we will be announcing the result of that consultation shortly.”