Parties are keeping voters “in the dark” about their plans for the economy, experts warned in a scathing analysis of the lack of detail in manifesto deficit-reduction promises.
The independent Institute for Fiscal Studies said there were “genuinely big differences” between the rival approaches on the key battleground issue but urged clarity on the tax and spending measures.
It delivered ammunition for each side in the bitter battle - suggesting the Tories would have to make swingeing cuts to services and Labour borrow £26 billion a year.
And in a blow to the Scottish National Party, it said there was a “significant disconnect” between its claims to be an anti-austerity party and plans that implied it would be spending less than Labour by 2019/20.
“They would cut less to start with but the implication of the plans they have spelt out in their manifesto is that the period of austerity would be longer than under the other three parties we consider,” it said.
SNP leader Nicola Sturgeon has accused Ed Miliband of offering a “Tory-lite” economic plan.
The thinktank’s verdict was delivered amid renewed hostilities over the economy, with Labour saying Tory cuts would be bigger than in any of the world’s advanced economies.
Ed Miliband is warning the scale of the Conservative squeeze would be unprecedented in any three-year period since demobilisation at the end of the Second World War.
But Chancellor George Osborne hailed official figures showing he beat his target for reducing annual public sector borrowing for the latest financial year by nearly £3 billion as proof his plan was working.
The result undershot the latest target of £90.2 billion set by the independent Office for Budget Responsibility (OBR) at the time of last month’s Budget and is an overall fall of £60 billion since 2009/10.
Mr Osborne, campaigning in the seat of his Labour shadow Ed Balls, said voters were “owed a real explanation of the real choices on offer” as he cited Treasury analysis that the SNP would add £6 billion to Britain’s debt interest payments.
“In this election there seems to be a fatigue with big numbers. Our £30 billion of savings, their £148 billion of extra borrowing,” he said.
“Who knows what the real numbers are?, people say. But saving £30 billion is not the same as borrowing an extra £148 billion. There is a massive difference in a country whose budget is £740 billion a year.
“Saving money means taking the difficult decisions so we reduce our debt and keep our economy out of crisis and on an even keel.
“Borrowing much more money involves higher national debt, higher debt interest costs and higher taxation, either now or deferred in the future
“So surely, with just two weeks to go to polling day and with millions already voting by post, the public are owed a real explanation of the real choices on offer and the consequences for their jobs, their incomes, their mortgage bills and the stability of the British economy. I think so.”
Presenting its findings, IFS deputy director Carl Emmerson said: “There are genuinely big differences between the main parties’ fiscal plans.
“The electorate has a real choice, although it can at best see only the broad outlines of that choice.”
Conservatives say they would eliminate the deficit by 2017/18 and start to run a surplus while Labour says it will reduce the deficit each year and balance the books “as soon as possible” during the five-year term.
The IFS said the Tory plans were “predicated on substantial and almost entirely unspecified spending cuts and tax increases”, and could involve “further real cuts to unprotected departments of around £30 billion”.
Labour’s plans were consistent with a pledge not to borrow for day-to-day spending but “would leave borrowing at £26 billion a year in today’s terms”, it said.
The IFS said the Liberal Democrats had been more transparent about overall fiscal plans to 2017-18, revealing that they are aiming for a tightening more than Labour but less than the Conservatives.
On a campaign visit to Cornwall, Prime Minister David Cameron said: “What the IFS show is that a Labour government would have to borrow £90 billion more. That would be a risk to our recovery, a risk to our economy, a risk to jobs.
“We can stop that by voting Conservative on May 7.
“Our plan is a continuation of what we have done over the last five years, when we have turned the country around, got the deficit down, put the country back to work and are seeing a successful economy.”
Mr Miliband dismissed the IFS calculation that Labour’s plans could increase the UK’s debt by £90 billion.
“The IFS assumptions are based on three different things, which I frankly don’t accept,” he said on a campaign visit to Nuneaton.
“The first is based on the idea that when it comes to our plan it’s not simply the budget in balance, which is what they say our plan is, we want a current surplus.
“Secondly, they pick out a particular year for when we are going to achieve it.
“And thirdly, I don’t accept this point that the Tories are even going to achieve their plans.”
The IFS had confirmed Labour warnings about the consequences of a Conservative victory on May 7, he said.
“We have now had it confirmed today that they want to have the most extreme cuts in the developed world, confirmed by the Institute of Fiscal Studies.
“Our is a better plan, a balanced plan and the right plan.”
Mr Osborne insisted the Tories had put forward a “balanced and clear plan” and seized on the IFS conclusion that Labour could “leave the British government less well placed to deal with future adverse effects”.
“In other words, we will be more exposed to the economic storms,” he said.
“Britain has been through those economic storms before, we don’t want to go through them again.”
He went on: “We face this choice in our country, a choice coming in two weeks’ time: do we get straight back to work on an economic plan that is working under David Cameron; or do we have the profound instability of a Miliband/SNP government borrowing more - as confirmed today by the IFS - and a dangerous cocktail of higher interest rates, higher mortgage rates, lost jobs and lost incomes.”
Mr Clegg said the IFS had identified the Tory plans for a “secret cuts bombshell”.
Speaking in Talgarth, Mid Wales, Mr Clegg told the BBC: “The IFS, they have advice and sharp words for all parties, but they nonetheless acknowledge that the Liberal Democrats have been more transparent, more open, more overt with the British people about the choices needed to balance the books and do so fairly.
“They confirm, as we have been saying, that we will cut substantially less than the Conservatives’ ideological plan to cut many public services to the bone and borrow less than the reckless plan from the Labour Party.
“But third, and perhaps most dramatically today, I have never heard the IFS provide such stinging criticism of any major political party - they say the Conservatives’ plans are misleading.
“They are indeed misleading, because the Conservatives have a secret cuts bombshell that will hurt the most vulnerable in society and will take millions and millions of pounds away from the public services that people rely upon.”
Liberal Democrat spokesman David Laws said: “The IFS could not be clearer - when it comes to the economy the Liberal Democrats are the most transparent and are the party that will end austerity the earliest.
“By contrast, the IFS lift the lid on Tory plans to cut public spending to the bone and accuse them of burying details of their the plans to shrink the state.
“They also shine a light on the sheer scale of Labour’s deficit denial, which includes yet unspecified levels of borrowing, despite starving the NHS of the cash it needs.
“It’s now official. Only the Liberal Democrats can be trusted to build a stronger economy and fairer society, and create opportunity for all.”
Mr Balls highlighted the IFS conclusion that the Tories “risk giving a misleading impression of what public service spending under a Conservative government would look like”.
“The truth the Tories won’t admit is their plans are so extreme they would end up cutting the NHS. Countries which have cut spending on this scale have cut their health service by an average of 1% of GDP - the equivalent of £7 billion.
“The IFS also warns that Tory plans would mean radical changes to tax credits and child benefit. George Osborne must now come clean on his secret plans to take money away from millions of working families.”
A Ukip spokesman said the decision by the IFS not to examine its policies was “testament” to its decision to have its manifesto looked at by the independent Centre for Economics and Business Research.
“In this election it was Ukip that set the gold standard by ensuring, before release, that our manifesto was not just sensible, serious and practical, but was fully costed and did not promise anything that couldn’t be delivered,” he said.
SNP Finance Secretary John Swinney said the contention the SNP would spend less than Labour was “ludicrous” and based on “flawed” assumptions.
“When Labour have publicly said they will introduce cuts across departments and have voted to meet Tory budget plans - claims they would spend more than the SNP are simply ludicrous,” he said.
“The reality is there are flaws in the IFS analysis of SNP plans. The IFS have assumed SNP borrowing would be the same as Labour’s borrowing in 2019/20. That is wrong.
“Our plans would see borrowing not at 1.4% like Labour but at 1.6% that makes the IFS analysis of our plans deeply flawed.
“And while the IFS praise the SNP on one hand for not making up figures on tax avoidance they have allowed Labour and the Tories to get away with basing their plans on what it admits are ‘unspecified’ and ‘largely made up assumptions’. That is simply ridiculous.
“Nor do they include money that would be saved in the next parliament by not renewing Trident for spending on education, health and childcare.
“SNP plans will see real terms increases in government spending, not cuts. We will protect the NHS and provide the support for those who need it.”