Senior Tories have refused to reveal the full cost of their spending plans as the chancellor was plunged into a “fake news” row over a dossier claiming Labour would rack up a £1.2 trillion bill in government.

Sajid Javid ​said Labour would bring the country into “an economic crisis within months” as he doubled down on a Tory analysis which claimed Labour would go on a multi-billion pound public spending spree over the next parliament.

But the chancellor would not say how much his own plans would cost – and refused to be drawn on what tax and spend measures would be contained in the manifesto.

Labour said the 35-page dossier, which was overseen by Mr Javid, was “an absolute work of fiction” as both parties slogged it out over their economic offer to voters.

Mr Javid repeatedly refused to be drawn on the overall cost of Conservative pledges, telling the BBC’s Andrew Marr Show: “We will set out our plans during the course of this election campaign.

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“When we publish the manifesto you’ll see what we’ve got to say on tax, but what I’ve already said and I said just last week, is that with our plans, because they are properly costed and by the way whether it’s a tax pledge or anything else, we will be clear about how we will be funding that and that will be absolutely inside our fiscal rules.”

He refused to say whether the Tory manifesto would contain tax cuts hinted at by Boris Johnson during the Tory leadership race.

Pressed on Labour’s rebuttals, Mr Javid said: “Of course John McDonnell, Jeremy Corbyn aren’t going to welcome these numbers. They don’t want to see this kind of transparency.

“These are eye-watering levels of spending – 1.2 trillion.

“It will be absolutely reckless and will leave this country with an economic crisis within months. Not years, within months.”

Business minister Kwasi Kwarteng also refused to say discuss Tory plans while attacking Labour, saying: “I’m not going to bandy around figures.”

The document was worked up by Tory researchers based on costings for Labour’s 2017 manifesto and its recent spending pledges, spread out over a five-year period.

The Conservatives claim Labour’s 2017 manifesto pledges cost more than £610m and tots up some £585m in pledges since then.

These figures include the CBI’s claim that Labour’s nationalisation plans would cost £196bn – a figure the party has robustly disputed.

Analysis of the dossier shows it also assumes Labour would immediately sign up to the 32-hour week, abolish private schools, and pilot a universal basic income.

None of those policies have been approved by senior Labour figures, who will hold a meeting to rubber-stamp the manifesto next weekend.

Mr Corbyn and Angela Rayner, the shadow education secretary, have both committed to removing charitable status and tax breaks from independent schools, but stopped short of endorsing the abolition of private schools which was voted for at the party’s annual conference.

John McDonnell condemned the report as a “ludicrous piece of Tory fake news”, made up of an “incompetent mish-mash of debunked estimates and bad maths”.

The shadow chancellor said: “Labour will tax the rich to pay for things everyone needs and deserves, like decent housing, healthcare and support for our children.”

Andrew Gwynne, Labour’s campaign coordinator, said the £1.2 trillion claim was an “absolute work of fiction” by Tories, adding: “You can’t trust a word that Johnson and his ministers say on this issue.

“We will have a fully-costed manifesto in due course when we launch that, and the challenge actually is for the Conservatives to fully cost their own manifesto, something they didn’t do in 2017.”

The row comes after Mr McDonnell and Mr Javid went head-to-head with speeches last week, setting out their ambitious spending plans to woo voters.

Mr McDonnell is understood to be keen to have a TV debate with his Tory counterpart about spending plans, with sources saying he has given the nod to two broadcasters.

Sir Ed Davey, the Lib Dem Treasury spokesperson, called on both parties to submit their manifestos for independent scrutiny rather than throwing around cash commitments.

“These flush figures are a knee-jerk reaction fuelled by fantasy Brexit-economics, failing to acknowledge the drain on our resources that Brexit has, and will continue to be on our public services,” he said.