With the escalating cost of HS2, a changed political landscape and greater awareness of environmental concerns, the arguments for high-speed rail are having to be remade.

But the underpinning belief articulated by the Conservative-led coalition government in backing HS2 should still hold sway, argue those who believe this is an important way of “levelling up” the regions.

The aim, spelled out in a 2013 strategic case, was to “build a stronger, more balanced economy capable of delivering lasting growth and widely shared prosperity”. And transport links were seen as critical for economic success, particularly high-quality infrastructure that would join up cities around the country.

Between promoting domestic air, road or rail travel, the latter was seen as easily the best choice. A new, high-capacity rail line would move as many passengers as two three-lane motorways, and beat other modes of transport by running straight into city centres. The question became what kind of railway to build.

Rail passenger numbers had doubled in 20 years to 1.5 billion when HS2 got the green light in 2012-13; another 15% have since squeezed on. Particularly rapid growth came on the west coast mainline, where fast trains compete for space with stopping services and freight. An upgrade of that line had already been carried out, coming in at triple the budget and causing enormous disruption over a decade of work. Meanwhile, growing congestion meant peak-hour trains were overcrowded in Birmingham, Leeds, Manchester and Sheffield as well as London.

HS2 was intended to free up space everywhere and be the core and spine of a modern, electrified national railway. This is a track that planners hope will be used in future centuries, like the railways 21st century Britain inherited from Victorian engineers. The idea that the technology would not be the best available, or trains would run much slower than was possible, was seen as perverse.

For many people, good local connections will indeed be more important than intercity travel. But Maria Machancoses, speaking for the Midlands Connect transport body, told the Lords economic affairs committee last week that the choice of local links or HS2 was a false one: in many places, they exist in tandem.

Supporters of HS2 argue that plans to develop connections within the Midlands are enabled by the project. Fast trains will go to a new Birmingham Curzon Street station on a new track, freeing up capacity for New Street station to be the more efficient hub of the currently struggling regional network. Large parts of the Northern Powerhouse Rail plans are likewise contingent on HS2.

The cost-benefit ratio of HS2, as calculated by the Treasury rulebook, has never been in any way compelling, starting at £2.30 back for every £1 invested; and as the bill has gone up, the calculation grows ever worse. But that analysis only captures the existing populations and markets, rather than the transformation that proponents argue HS2 will bring to the places where people live and work and the journeys they take.

Economists and planners believe quick, reliable transport links spell jobs and growth. Other big infrastructure developments, such as the eastern Jubilee line in London, have had poor cost-benefit assessments (and escalating budgets) – but within 13 years of the opening of the tube line extension in 1999, the number of jobs at Canary Wharf went up fourfold to more than 100,000 as companies relocated.

Towns on the route of HS1, the short existing high-speed line in Kent, have seen increased investment in businesses and homes. The promise of HS2 alone has driven signs of a rebalancing economy in Birmingham, including booming construction and the relocation of major firms such as HSBC.

Although HS2 prefers to emphasise capacity rather than speed, the evidence suggests businesses, and individuals, do indeed value getting to Birmingham quicker.

Passengers pay a huge premium on tickets to use faster intercity services between the Midlands and London: roughly double the fare of rival trains to save 15%-30% of the journey time.

All parts north-west from Crewe would see journey times to London slashed when services are integrated in 2031; the complete HS2 network would make new connections easy – such as the north-east to the Midlands – let alone bringing Manchester to just 67 minutes from London.

The city leaders along the route firmly believe regeneration will accompany the new line. Visions of transformation naturally exist for Old Oak Common (at the southern end of the development) and Birmingham, where bulldozers have already prepared the ground, and around the high-speed hubs of Manchester and Leeds; but also in places such as Darlington and Durham, where business plans are being drawn up for the knock-on effects of improved transport links.

Meanwhile, according to HS2, the construction of the line itself will employ about 30,000 people at its peak.

The time and money (about £7.4bn) already directly spent may be sunk costs. But cancellation might spell a long wait for better links, even in the event that the savings were indeed ringfenced for transport in the regions.

To get HS2 “shovel-ready”, more than a decade has passed with extensive public consultation, parliamentary scrutiny and engineering studies carried out – including examining the kind of incremental upgrades proposed again now. A similar period of scrutiny and debate would likely await alternative schemes.

HS2, even with delays, should be running high-speed services to Crewe and beyond by 2031, a timeframe that its supporters insist is unlikely to be achievable for any comparable alternative.