Is the Lower Thames Crossing the New HS2?

HS2 has become shorthand for infrastructure failure in the UK. Sadly, lessons have not been learnt, and the Lower Thames Crossing (LTC) could soon become the new poster child for infrastructure project failure.

Mile for mile, the LTC is likely to be more expensive than HS2. The latest LTC cost estimate is £11 billion for 14.3 miles of ‘smart’ motorway and tunnel, making it £769 million per mile. Remarkably, construction has started on the Lower Thames Crossing (LTC) without a final business case in place – just as it did with HS2!

A final business case is essential. It tells the public whether a project actually makes economic sense. Starting construction without one is not ‘cutting red tape’, it is being reckless with public money.

When HS2 was first approved, its champions insisted the numbers were solid. However, costs spiralled out of control, too little was done to tackle this, and the project passed the point where politicians could easily walk away from it. Finally the current government has tried to grapple with the specifications and costs, but billions have already been wasted.

The LTC is following the same path. In February 2025, after many rises already, National Highways estimated the total cost at £9.4 billion. By December 2025 – just nine months later – that figure had jumped to almost £11 billion. The private investment required had grown from £6.3 billion to £7.5 billion, an increase of 19%, while the public contribution will be at least £3.1bn.

Starting work on LTC without a final business case, just like HS2

There have been many warnings, so the government will not be able to claim ignorance. We wrote to the National Audit Office in March 2026, warning of the financial irregularities of the LTC and the dangers of starting publicly funded construction works without a final business case in place to ensure the project represents good value for money.

This is also highlighted in Sir Stephen Lovegrove’s recent report on HS2 – that starting work prematurely on large infrastructure projects without a full understanding of the business case can lead to rapidly escalating costs.

Following this, the chair of the Transport Committee, Ruth Cadbury, said the problem with HS2 was “not just the speed, but also that spades were in the ground before the project had been fully designed, permits granted and so on”. She also asked Transport Secretary Heidi Alexander how she would prevent LTC and Northern Powerhouse Rail “going the same way” as HS2. Pointedly Ms Alexander’s response only talked about Northern Powerhouse Rail and she failed to mention the LTC…

A benefit-cost ratio that doesn’t add up

Before the latest round of cost increases, the LTC’s benefit-cost ratio (BCR) stood at just 1.22 — meaning that for every pound spent, only £1.22 of economic benefit was expected in return. That is a threadbare return for a project of this scale, and every increase in the project’s price tag erodes that ratio further. Rather than review the scheme, the government has raised the value of road freight to fix the numbers and make the scheme seem a better bet.

Compare this to the Ely Area Capacity Enhancement Scheme, a rail improvement project in Cambridgeshire that would genuinely open up freight and passenger routes across the country and remove much traffic, especially HGVs, from our roads. Its BCR is 4.89. In other words, it delivers four times the economic return per pound spent as the LTC. Yet the Ely scheme struggles for funding while the government pours billions into a giant hole under the Thames.

The toll trap

One of the less-discussed dimensions of the LTC is what it will mean for everyday drivers at the Dartford Crossings. The private finance model that underpins the LTC relies on tolls to repay investors. The government has already said it will give away the existing Dartford Crossings to the developer of the LTC, along with all its toll income. If that wasn’t bad enough tolls at both Dartford and the new crossing could triple to pay for the construction costs and for the developer’s profit. We have already seen a 40% hike in Dartford toll charges in September 2025, raising the basic car charge from £2.50 to £3.50. If our projections are correct, that is just the beginning.

Will the government learn from HS2 mistakes?

HS2 shows that it is possible to get so far into a project that cancelling it becomes politically unthinkable, even when the economics no longer stack up. That is the position the government appears to be hurtling towards with the LTC, by committing billions of public money and starting work before a final business case has been completed or private finance secured.

The government has already acknowledged that the difference in terms of value for money between a privately funded and a publicly funded and owned LTC is “marginal”. They further admitted that if tolls rise too much then the publicly funded option would become better value for money. However, without a final business case in place, how will they know whether either option makes sense, and how likely is it that they’ll pull out of protracted negotiations and contracts with private investors?

The responsible thing would be for the government to pause work on the LTC, complete the final business case, and consider whether public money could be better spent (alternatives to a ‘smart’ motorway do exist).