A Corbyn Government would plunge Britain into an economic crisis "within months," Sajid Javid has warned after Conservative HQ calculated the Opposition’s policies would cost £1.2 trillion – an estimate dismissed as an “absolute work of fiction” by Labour.

The Chancellor claimed the Opposition would spend an extra £650 million a day if they won the General Election, describing the levels of spending as "eye-watering".

But Labour swiftly hit back, condemning the analysis as a "ludicrous piece of Tory fake news" and an "incompetent mish-mash of debunked estimates and bad maths".

Mr Javid said the proposals - which include plans to renationalise rail, mail, water and energy - were "absolutely reckless" and equivalent to funding the entire NHS budget for nine years.

He told BBC One's The Andrew Marr Show: "This is the true cost of Corbyn's Labour: these are the numbers that John McDonnell did not want you to see, and they're out there today...

"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," declared the Chancellor.

But John McDonnell said: "Labour will tax the rich to pay for things everyone needs and deserves, like decent housing, healthcare and support for our children.

"We will also use the power of the state to invest to grow our economy, create good jobs in every region and nation and tackle the climate emergency.

"The Conservatives will be able to read all about these plans - and how much they actually cost - when we publish our fully-costed manifesto," explained the Shadow Chancellor.

The analysis, overseen by Mr Javid, is based on costings for Labour's last manifesto and its most recent pledges, spread across a five-year period.

Andrew Gwynne, the Shadow Communities Secretary, also dismissed the Tory calculations out of hand, saying they were an “absolute work of fiction” and stressed Labour’s manifesto – to be agreed at a so-called Clause 5 meeting next Saturday – would be “fully costed” and the most radical since the Atlee Government of 1945.

But his colleague Nia Griffith, the Shadow Defence Secretary, said Labour would not implement every policy from its annual conference as the party could "only do a certain amount at once".

Meanwhile, Kwasi Kwarteng, the Business Minister, was unable to put a price on his own party's pledges, telling Sky News’s Sophy Ridge on Sunday: "I'm not going to bandy around figures."

The economic row came as:

*party leaders displayed a rare moment of unity as they paused their campaigns to pay their respects at the National Service of Remembrance at the Cenotaph;

*Mr Gwynne refused to say whether a Labour Government's Brexit deal would end freedom of movement;

*Credit ratings agency Moody's lowered its outlook for UK debt to "negative" from "stable" and

*Mr Kwarteng said Boris Johnson was right to claim there would be no barriers to trade crossing the Irish Sea after Brexit.