CONSERVATIVES and Labour have been warned about “abandoning restraint” after they each promised to unleash a spending splurge running into tens of billions of pounds every year - to win votes.

One former Treasury chief accused them both of fiscal incontinence.

Sajid Javid signalled he would rip up the Treasury rules on tax and spending to enable Government to take advantage of low interest rates to borrow more to realise an “infrastructure revolution”.

This, the Chancellor told a campaign event in Manchester, would enable a future Tory administration to “build new hospitals, schools, roads, railways and better broadband”.

Over the next five years, his “new economic plan for a new economic era” would free up £100bn.

The respected Institute for Fiscal Studies said the Tory plan to raise the cap, which keeps borrowing below two per cent of national income, to three per cent would be the “highest level sustained at any point in the last 40 years”.

However, John McDonnell, Mr Javid’s Labour Shadow, went further. In a campaign speech in Liverpool, he announced Labour would loosened fiscal constraints even more to allow £55bn a year of new investment, more than doubling current levels; over a five-year parliament that is £275bn.

Announcing an “irreversible shift” of investment away from the UK capital to northern England and Scotland, Mr McDonnell said: “That means change, real change, and it means investment on a scale never seen before in this country and certainly never seen before in the north and outside of London and the south-east.”

The IFS noted how Labour’s spending plans would more than double public investment expenditure to an “unprecedented” level since the very different era of the 1970s.

Ben Zaranko, the think-tank’s research economist said: “Both parties’ plans would represent a sharp change in policy and Labour’s plans are especially ambitious."

He explained the key challenge for a government seeking to deliver investment on this scale would be finding worthwhile and viable projects in which to invest.

“Shortages in the number of suitably skilled construction workers, a dearth of ‘shovel-ready’ projects, and practical issues relating to delivery will be challenges the next government will need to think carefully about how to overcome,” added Mr Zaranko.

Syed Kamall, Academic and Research Director at the Institute of Economic Affairs, said: "Today's election speeches show both parties have abandoned fiscal restraint in favour of increases in public spending to be paid for through extra borrowing.

“The Shadow Chancellor has pledged to more than double government borrowing from £25bn a year to a staggering £55bn, proposing massive increases in spending and state intervention in the economy.”

He noted that while Mr McDonnell had promised an overhaul of infrastructure, “grand government projects,” like the massively over-budget HS2 project, were notoriously inefficient.

Mr Kamall also picked up on the point about strategy.

He explained: “Promising billions of additional spending on the NHS without also thinking about the best structures and systems to deliver better patient care and choice will do nothing to fix the long-term problems facing the health service. If spending doesn’t go hand-in-hand with reforms, the NHS will continue to lag behind other EU countries in terms of healthcare outcomes.”

Noting how Mr Javid had also chosen to revise his fiscal rules in favour of hikes to public spending funded through more borrowing, the IEA director added: “While it is positive that the Chancellor stressed the importance of keeping debt in check, turning on the spending taps risks undermining the work of recent years to get the budget deficit under control, after years of over-spending.”

Lord Macpherson, the former Treasury Permanent Secretary under the Blair, Brown and Cameron governments, tweeted: “Have the fiscal proposals of the 2 main parties ever been so incontinent? Borrowing to invest is only sensible if it does not result in ever increasing debt. Not too late for the Lib Dems to provide some Gladstonean rigour.#soundmoney.”

Sir Ed Davey, the Liberal Democrats’ economics spokesman, said: “Neither Labour nor the Tories can square their spending promises today with the cost of Brexit. They are writing promises on cheques that will bounce.”

He added, in contrast, his party would stop Brexit and invest a £50bn Remain bonus in public services.