The national infrastructure strategy to invest £100bn in boosting the economy and tackling the climate crisis is expected to be delayed until after the budget.

The plan to improve transport connectivity and work towards achieving net-zero emissions by 2050 had been set to be published “alongside” the budget, which is due on Wednesday.

But the chancellor, Rishi Sunak, who took over at the Treasury last month, is not expected to unveil the plans seen as being crucial to the government’s “levelling up” agenda until a later date.

Whitehall sources were unable to say when it would be published, but expected the delay to be only a matter of days or weeks.

However, the shadow chancellor, John McDonnell, said the delay represented “absolute chaos” in government.

“We are facing the threat of climate change and an economy at risk of recession. That’s why we desperately need an immediate start to large-scale infrastructure investment,” he said. “Delaying implementation of investment is unacceptable.”

Sir John Armitt, the chair of the national infrastructure commission, said they were “disappointed” at the delay but expressed confidence that ministers remained committed to infrastructure investment.

“Naturally we are disappointed about the further delay in the government’s formal response to the national infrastructure assessment, which we published over 18 months ago,” he said.

“However, we are encouraged by the evident focus the government wishes to place on investing in the UK’s future infrastructure.

“Prioritising that investment within a long-term plan is key to success and if a short delay leads to a better strategy that more comprehensively addresses our recommendations, it will be worth the wait.”

A Downing Street spokesman said: “It is vital that we give these decisions the proper time and care they deserve. The national infrastructure plan will follow in the coming months and government officials are working on it as a priority.”