Britain is heading back to a "1970s-sized state" in terms of public service spending, whoever wins next month's general election, a new report claims today.

As the political parties prepare to hit the campaign trail after the dissolution of parliament on Tuesday, the Resolution Foundation claimed both parties will "turn the spending taps back on".

The think-tank's new analysis suggests that even just maintaining public service spending as a share of the economy could mean overall expenditure rising to 41.3 per cent of GDP by 2023.

This, the researchers add, is largely down to chancellor Sajid Javid's plans for significant increases in infrastructure spending, and is well above the average of 37.4 per cent recorded average in the two decades before the financial crash.

The organisation added that with further spending increases on key pubic services such as the NHS, a future Conservative government is likely to be above 1970s levels in terms of public service spending.

Top 10 marginal seats to watch at the general election Show all 10 1 /10 Top 10 marginal seats to watch at the general election Top 10 marginal seats to watch at the general election North East Fife Currently held by the SNP with a majority of 2 Getty Top 10 marginal seats to watch at the general election Kensington Currently held by Labour with a majority of 20 Getty Top 10 marginal seats to watch at the general election Perth and North Perthshire Currently held by the SNP with a majority of 21 Getty Top 10 marginal seats to watch at the general election Dudley North Currently held by independent, formerly Labour, MP Ian Austin with a majority of 22 LivingInMediocrity Top 10 marginal seats to watch at the general election Newcastle-under-Lyme Currently held by Labour with a majority of 30 Derek Harper Top 10 marginal seats to watch at the general election Southampton Itchen Currently held by the Conservatives with a majority of 31 Rob Candish Top 10 marginal seats to watch at the general election Richmond Park Currently held by the Conservatives with a majority of 45 Robin Webster Top 10 marginal seats to watch at the general election Crewe and Nantwich Currently held by Labour with a majority of 48 Jaggery Top 10 marginal seats to watch at the general election Glasgow South West Currently held by the SNP with a majority of 60 Alec MacKinnon Top 10 marginal seats to watch at the general election Glasgow East Currently held by the SNP with a majority of 75 Christine Johnstone

It comes after the senior treasury minister, Rishi Sunak, rejected suggestions the Tories were "spending money like water" in their policy commitments on the BBC's Andrew Marr show.

John McDonnell, the shadow chancellor, also insisted on the same programme that Labour would produce a manifesto alongside a costings booklet, detailing where the funds for each pledge would come from.

The report, published ahead of the first December general election in almost a century, said Labour's plans could result in government spending as a share of GDP rising significantly above the 1970s average.

"Recommitting to the £48.6 billion of extra current spending announced in the 2017 manifesto, coupled with shadow chancellor John McDonnell's £250bn ten-year capital plan, would mean government spending as a share of GDP rising to 43.3 per cent," the researchers noted.

"After an unprecedented decade of austerity, both main parties are gearing up to turn the spending taps back on," said the foundation's chief executive Matt Whittaker.

He added: "The shared commitments to ending austerity, reversing elements of it, and big infrastructure plans mean that Britain could be heading back to a 1970s-sized state, whoever wins the next election.

"It's important that parties set out detailed economic strategy in their manifestos that reflects the changing size and shape of the state, and the big demographic pressures to come.