Rishi Sunak’s £36bn plan to replace the northern leg of the HS2 rail link is not fully costed and beset by uncertainties, industry experts have warned, as they and local leaders attempt to unpick the policy.

After being unveiled by the UK prime minister last month, “Network North” was billed by the government as a “tidal wave of new investment” that would better connect parts of the North of England.

Sunak said the rail, road and bus schemes would be a better use of public money than the second leg of the high-speed rail line, which was due to run from Birmingham to Manchester.

HS2, whose budget has ballooned in recent years, will now stretch between Birmingham and London, though it is unclear whether it will run into the heart of the capital.

But transport experts and local leaders told the Financial Times that many schemes had not been properly costed and lacked business cases or delivery timeframes. Some depend on other major investments, such as the expansion of northern railway stations, which have yet to be announced.

Sir John Armitt, chair of the National Infrastructure Commission, a government advisory board, said Network North was an instance of the UK “acting in haste with a clear risk of repenting at leisure”.

Some of the project’s schemes had “not been designed in any sense of detail whatsoever”, he said, adding that some costings seemed to have been “plucked out of the air”.

If the government was “serious” about cutting the northern leg of HS2, “it needs to be serious about what’s going to replace it. Otherwise, why would anyone in the Midlands or the North have any confidence in it?” Armitt said.

The centrepiece of Sunak’s Conservative party conference speech, Network North consists of a range of transport schemes across the country, weighted towards the North and Midlands.

Dame Bernadette Kelly, the top civil servant at the Department for Transport, told the House of Commons public accounts committee this month that Downing Street had asked the ministry to start work on the plan in late August, in strict confidence.

With civil servants barred from seeking external advice, according to Kelly, Sunak’s announcement took transport delivery bodies and the rail industry by surprise.

According to analysis by the Rail Industry Association, less than one-third of the funding originally allocated to HS2 — roughly £11.65bn — had been reallocated to Network North rail schemes.

Just under 25 per cent had been earmarked for road resurfacing, while about one-third comprised an increase in transport funding to local authorities and mayors, which may or may not result in new light rail schemes.

Darren Caplan, chief executive of the representative body, said Network North had been drawn up “without consultation with the railway industry, or an assessment of project value-for-money or risk”. He added that the plan represented “a very significant real-terms cut to overall rail spending”.

The RIA analysis found that most of the plan’s rail projects had already been announced and identified only five brand new proposals. All of the projects in the plan are still subject to business case approval by Whitehall.

One of the largest of the new proposals is the proposed electrification of the North Wales mainline, costed in the plan at £1bn.

Mark Barry, professor of practice in connectivity at Cardiff University, said no detailed business case had been done since 2015, and that such a proposal would cost more than £1bn when upgrades to Victorian branch lines around Chester were factored in.

The priority for leaders in North Wales was not rail electrification but increasing line speeds and expanding “seriously” constrained capacity at Chester station, he said.

UK ministers did not consult Network Rail, which is responsible for Britain’s rail infrastructure, the Welsh government or the country’s new rail board, a joint policy body for Cardiff and London, ahead of the announcement. The Labour-led Welsh government called the lack of a consultation “deeply disappointing”.

The transport department said the North Wales project was part of a “massive investment in roads and local transport” that would benefit communities across the North and Midlands “more quickly than would ever have been the case under HS2”.

About one-third of Network North comprises funds for mayors and local authorities in England, designed for use on locally developed public transport proposals such as new buses, trams and tram-trains.

Some of the funding is not expected until the early 2030s, however, including the bulk of the extra cash allocated for a long-awaited mass transit network in West Yorkshire.

Nevertheless, the uplift in local mayoral funding was broadly welcomed by northern leaders. Lord Ben Houchen, Tory mayor of Tees Valley, said HS2 would have not have benefited his constituents but Network North had “freed up billions of pounds to be spent on real tangible projects”.

Oliver Coppard, Labour mayor of South Yorkshire, also welcomed an increase in local funding of roughly £540mn from 2027 but cautioned that some big announcements could only happen “if the stations are upgraded as much as the lines themselves”.

Otherwise it was “like building new roads between two car parks that are already full”, he said.

One local official closely involved in transport projects in the north of England said the increase in funding to mayors had been somewhat “lost in the noise” of poor communications.

That included an initial announcement by the government that it would reopen the Leamside line. Closed in the early 1990s, the route has long been identified as a mechanism for diverting freight off the East Coast Mainline.

Ministers later said it could be paid for with the region’s extra transport cash, but local leaders say there is unlikely to be enough money to reopen the route, which they view as a key national infrastructure project.

Sunak’s axing of HS2’s northern leg also has consequences for Northern Powerhouse Rail. The long-planned, high-speed east to west route was in part contingent on the rail link tunnelling through Manchester.

The government has earmarked £12bn towards NPR in Network North in light of that, but no extra money has been made available to build the kind of stations that Manchester and Liverpool believe are necessary to meet current and future capacity.

Local politicians hope some form of new financial mechanism — potentially using land value capture — might fill the gap. Steve Rotheram, mayor of Liverpool city region, said he was willing to work “creatively” with ministers about the new version of NPR, whose original version was announced only two years ago.

Kelly told MPs it would be “some time” before a new business case for NPR would be complete.

The transport department said the £12bn would allow NPR to be delivered “as previously planned”, adding that it would “continue to work with local leaders”. It added Network North “is funding vital rail projects in the north and midlands”, which were “over and above” the government’s last rail strategy from 2021.