NAO to Scrutinise Lower Thames Crossing as Questions Grow Over £11bn Project

The National Audit Office (NAO) is preparing to investigate the Lower Thames Crossing, signalling increased scrutiny of one of the UK's largest and most expensive transport infrastructure schemes as concerns continue to mount over escalating costs, funding arrangements and long-term value for money.

The move follows calls from campaigners for an independent review of the project, which will create a new 2.6-mile twin-bore road tunnel beneath the River Thames between Kent and Essex.

Although construction has yet to begin, more than £1 billion has already been spent on planning, development and statutory approvals, while the overall cost of the scheme is now estimated at around £11 billion.

Watchdog prepares formal review

In correspondence with campaign groups, NAO Comptroller and Auditor General Gareth Davies confirmed the spending watchdog is actively monitoring the programme and expects to undertake a formal investigation.

He wrote:

"I anticipate that I will examine and report on the Lower Thames Crossing. My teams are tracking activity on the programme. This will inform my decision on the right timing for audit work."

The NAO's role is to assess whether public money is being spent efficiently and whether major government projects are delivering value for taxpayers.

Project survives spending cuts

Despite widespread reviews of public spending, ministers recently confirmed that the Lower Thames Crossing would proceed after avoiding cuts made to other major infrastructure schemes.

The Government has committed £3.1 billion towards construction, with the remaining funding expected to come from private investment under a Regulated Asset Base (RAB) financing model.

Once operational, both the new crossing and the existing Dartford Crossing are expected to be operated by a private concessionaire under long-term regulatory oversight.

Construction is currently scheduled to complete in 2034.

Rising costs fuel criticism

The project has become increasingly controversial as costs have continued to rise.

Critics argue the scheme now carries one of the highest costs per mile of any major road project in the UK and point to the substantial expenditure incurred before construction has even started.

The Department for Transport took direct control of the programme from National Highways last year as part of efforts to strengthen governance and delivery.

For ministers, the project has also become emblematic of the wider challenges facing major infrastructure delivery in Britain, reinforcing calls for planning reform and faster decision-making.

Campaigners demand greater transparency

Transport Action Network (TAN), which has long opposed the scheme, welcomed the prospect of an NAO investigation but says it should begin immediately.

Chief Executive Abby Coften said:

"We're pleased the NAO agrees with us that the privatised Lower Thames Crossing needs investigating. However, this must be fast tracked before more public funds are wasted."

She added:

"The same mistakes are being made as on HS2, but worse, as LTC costs more per mile and has no completed business case."

Campaigners have also questioned proposals for future toll revenues to be collected by private investors rather than returning directly to the Treasury.

Government expects normal oversight

The Department for Transport sought to downplay suggestions that the investigation reflects concerns unique to the Lower Thames Crossing.

A department spokesperson said the NAO routinely examines major public investments and that it would be expected to review a project of this scale.

Similarly, the NAO stressed that it is continuing to monitor progress and will announce the formal launch of any audit once the timing is considered appropriate.

A pivotal moment for Britain's biggest road scheme

The announcement comes at a critical stage in the project's development.

With planning consent secured, funding arrangements taking shape and procurement moving forward, the Lower Thames Crossing is edging closer to construction.

However, the decision by the UK's independent spending watchdog to begin preparing for a detailed examination underlines the level of parliamentary and public interest surrounding the scheme.

For supporters, the crossing remains a once-in-a-generation investment designed to relieve chronic congestion at Dartford, improve network resilience and unlock economic growth across the Thames Estuary.

For critics, it has become another test of whether Britain can successfully deliver major infrastructure projects on time, within budget and with a compelling case for public investment.

The NAO's eventual findings are therefore likely to shape not only the future of the Lower Thames Crossing, but wider debates about how major transport projects are planned, funded and delivered across the UK.