Half a million jobs in the construction industry could be at risk if Boris Johnson gets his exit strategy from lockdown wrong, a trade body has warned.

With the prime minister promising to set out a “roadmapâ€� for restarting the economy on Thursday, builders are one of many sectors urging government to keep support going for long enough to allow businesses to get back off their knees – and then to open the spending taps to spark the economy back to growth.

Representatives of the brewing industry say that an abrupt end to state support could be fatal to pubs across the country. And retailers said that financial assistance will be needed for months after the exit from lockdown begins, as shopping gradually returns to normal levels.

It comes after Rolls Royce became the latest firm said to be considering redundancies – with the BBC reporting the aircraft engine producer could cut 8,000 UK jobs due to strain in the aviation sector.

In a letter to the prime minister, the British Chambers of Commerce called for a “carefully phased approach to lifting lockdown�, with the extension of loan, grant and furlough schemes for the immediate future, followed by an “expansionary� fiscal policy to stimulate the economy through investment funded by borrowing on a massive scale.

“This is a time to be bold,� wrote BCC president Ruby McGregor-Smith. “Government should not shy away from sustaining high levels of public spending in order to restart and renew our communities and the economy in the short and medium term, while not tying the hands of future generations.

“An expansionary fiscal policy, including a commitment to transformative infrastructure investment, will be needed in order to generate the returns that will help to pay down the national debt in the longer term.�

Federation of Master Builders chief executive Brian Berry stated that the construction industry looks set to be reliant on government investment projects for its return to profitability. With householders battered financially by the coronavirus lockdown and wary of allowing tradespeople into their homes for social-distancing reasons, it will take time for the renovation market to revive, he said.

“In the financial crash we lost 400,000 jobs and in the early 1990s it was 500,000,� said Mr Berry. “We will be looking at similar numbers to that unless the government pump-primes construction.

“That means the government making sure that infrastructure projects are being delivered and homes are being built.�