Rishi Sunak’s U-turns over net zero have delayed progress on vital infrastructure that is needed for economic growth, the government’s advisers have said.

Sir John Armitt, the chair of the National Infrastructure Commission (NIC), said good progress had been made on renewable energy in the past five years, but changes to key policies, including postponing a scheme to boost heat pump takeup, had created uncertainty and delay.

He said the government could no longer “duck key decisions”, as Britain was falling behind on vital infrastructure, from rail transport and energy to water, flood defences and waste.

Failure to catch up would stymie economic growth, and imperil climate targets, the NIC found in its latest annual review.

Since last September, when he watered down key net zero policies, Sunak has repeatedly referred to the need to be “pragmatic” on net zero.

Armitt said: “I can understand the need to seek to be pragmatic, but every time you seek to be pragmatic you take your foot off the gas and you provide an encouragement to people to say: ‘Well, do I really need to do this?’

“The message clearly has to be that this is something we’ve got to do if we believe in our carbon targets.”

He said heat pumps in particular, which the NIC found to be the only viable alternative to gas boilers for home heating, must be a top priority.

The NIC found:

• The government will fail to meet its targets on heat pump rollout.

• The promised lifting of a ban on new onshore windfarms has not gone far enough.

• Massive investment is needed in the electricity grid.

• There is no proper plan for rail in the north and Midlands now that the northern leg of HS2 has been cancelled, severely inhibiting economic growth in those regions.

• Water bills will need to go up to fix the sewage crisis, and more reservoirs are needed to avoid drought, while water companies have done too little to staunch leaks.

• The UK lacks a coherent strategy on flooding, with more than 900,000 properties at risk of river or sea flooding and 910,000 at risk of surface water flooding.

• Good progress has been made on the rollout of gigabit broadband around the country.

Armitt called for this government, and the next, to act swiftly. “It’s not too late to catch up in many of the areas we’ve highlighted, if the goals are matched with policies of sufficient scale. But the window is closing,” he said.

“Ducking big decisions over the next 12 months will put the major goals of net zero, regional economic growth, and environmental protection in jeopardy,” he warned.

Greater investment was needed in public transport, the NIC found. Uniquely in Europe, the UK’s second and third cities showed lower economic productivity than the national average, largely because of poor transport links, the review found.

The axing of the next phases of the HS2 high-speed rail project left a “critical gap” in rail connectivity between the Midlands and the north, with northern cities likely to “remain poorly served” without further investment.

Given long-term growth in demand “a do-nothing scenario north of the proposed connection of HS2 and the west coast mainline at Handsacre is not sustainable”, the report found.

The target of rolling out 600,000 heat pumps a year by 2028 to reach 7m homes by 2035 was way off track, the report found, while putting off a decision on hydrogen for home heating until 2026 had created uncertainty.

The next government should end new connections to Britain’s gas network from 2025, and ban the sale of new gas boilers for homes and fossil fuel heating in large commercial buildings by 2035, according to the report. It also called on the government to rule out subsidies for hydrogen heating.

These commitments should be underpinned by steps designed to make heat pumps more affordable for households, including sufficient funding, and a plan to shift the burden of policy costs from electricity bills to either gas bills or into general taxation.

Armitt stopped short of calling for force-fitting heat pumps and smart meters in a street-by-street programme – put forward earlier this month by Chris O’Shea, the chief executive of British Gas parent company Centrica – saying it was difficult to do “from top down” while maintaining public trust. He added that other low-carbon home heating options – such as heat networks – should also be considered in areas where they made sense.

The greatest challenge to the UK’s green electricity goals, according to the review, is the need to upgrade the country’s transmission infrastructure. The bottleneck of renewable projects waiting to connect to the grid has already increased costs for households. By 2030, network constraint costs are estimated to rise to between £1.4bn and £3bn a year, unless grid capacity is expanded.

A government spokesperson said: “We’re making sure we have the infrastructure we need to grow the economy, improve people’s lives, and tackle climate change – having already increased electricity generated from renewable sources to nearly half in 2023, giving more powers to cities to build the transport they need, and providing billions to tackle potholes up and down the country.”