Former chancellor Alistair Darling has urged his successor George Osborne to come up with “another plan” before “immeasurable” damage is done to the UK.
Mr Darling has written an open letter to the Chancellor, published in the Sunday People, in which he says that both men "have Britain's best interests at heart".
However, he continues: "But you and the Bank of England seem to have given up on any plan for growth.
"It's as if you're both saying there's nothing you can do and nature must take its course. But the damage that will do to our country is immeasurable.
"You really must act. And act now. Otherwise it will take years to get Britain's economy growing again to create the jobs we need. The need to get growth going - as the IMF recognises - is desperately urgent."
Mr Darling goes on to tell Mr Osborne that his first budget forecast is "hopelessly off course" and that his policies since 2010 "simply haven't worked".
He suggests "major spending projects" that would see investment in homes, power stations, railways and a third runway at Heathrow Airport.
The letter warns Mr Osborne: "You need another plan. Call it plan B. Call it whatever you like. But unless you do something now it will be years before we recover."
Mr Darling adds that Labour would be happy to work with the Chancellor on key issues like social care and welfare reform, citing youth unemployment as a priority.