Rishi Sunak, the Chancellor, will on Wednesday unveil the biggest public spending package on record as he pledges £600 billion to power "a decade of growth for everybody".

Mr Sunak will use his first Budget to set out what he describes as "the most ambitious investment in infrastructure and innovation ever" as he backs Boris Johnson’s election promise to "level up" the country.

Over the next five years, an average of £120 billion per year will be spent on roads, railways, broadband, housing and research, which Mr Sunak says is the highest real-terms public investment since records began in 1955.

The figure is £100 billion higher than the cost of the Government's existing infrastructure plans, suggesting that Mr Johnson may have set money aside for eye-catching projects such as a bridge or tunnel between Scotland and Northern Ireland.

Mr Sunak will also announce a package of measures to help the country get through the coronavirus crisis, but he wants the Budget to set out a vision of how the Conservatives could transform Britain if they stay in power for another decade or more.

By 2024, Mr Sunak will have tripled the average net investment of the past 40 years, with big-ticket items including the HS2 high speed rail line – predicted to cost £106 billion – and Northern Powerhouse Rail, known as the "crossrail of the north", at £39bn.

The Chancellor is expected to tweak the Government's fiscal rules to allow for more borrowing to pay for the spending splurge, partly designed to shore up Tory support in former Labour heartlands with an eye on the 2024 General Election.