The Chancellor George Osborne has warned he will have to find £30 billion in budget cuts and tax rises in the event the UK votes to leave the European Union.
In one of his starkest warnings against a Brexit yet, Mr Osborne said he would have to increase income and inheritance taxes and slash the NHS budget in an emergency Budget statement.
However, 57 Conservative MPs have said the Chancellor's position would be "untenable" if he cut NHS, police and school budgets.
Mr Osborne and Alistair Darling said the £30bn figure - made up of £15bn budget cuts and £15bn tax increases - is based on forecasts on the economic impact of a Brexit, made by the Institute of Fiscal Studies.
Among the tax rises would likely be a 2p rise in basic income tax and 3p rise in the higher rate. The Chancellor also warned that police, NHS, education and local government budgets could be cut by 5%.
Writing in The Times ahead of their speech, George Osborne and Lord Darling said: "We know all too well what happens when Britain loses control of its public finances.
"We're agreed that a vote to leave risks doing the same thing to Britain all over again."
Describing a Brexit as a "lose-lose" situation, Mr Osborne said: "As chancellor, I would have a responsibility to try to restore stability to the public finances and that would mean an emergency Budget where we would have to increase taxes and cut spending."