Future plans to improve a heavily-congested M25 junction at Brentwood have been thrown into doubt, following a decision to look more closely at the environmental impacts of the new road layout.

A Development Consent Order (DCO) for the go-ahead to improve the Brook Street M25 junction 28 with new loops and sliproads had been expected in December 2021, with work expected to start in the spring.

But the secretary of state is now extending the deadline to May 16 to allow for "further consideration of environmental matters".

A statement from National Highways, which is leading the programme, said: "The secretary of state for transport has asked for more time to make a decision on whether we can continue with our proposals to improve the M25 junction 28."

Specifically, the secretary of state has asked National Highways for an new assessment of the cumulative effects of greenhouse gas emissions from the scheme.

However National Highways says that, to conduct an impact assessment at a local or regional scale, some form of baseline would need to be identified to forecast carbon emissions over several areas - which has not happened.

The agency has replied: "There is no reasonable basis upon which National Highways can assess the carbon emissions impact of the scheme at a local or regional level, and it is not required to do by law or the National Policy Statement for National Networks.

"Accordingly, National Highways is not in a position to provide an assessment of the cumulative effects of the greenhouse gas emissions for the scheme for anything other than at the national level carbon budgets."

At peak times, up to 7,500 vehicles per hour pass through this heavily-used junction, resulting in queues and delays.

Highways England says the junction is heavily congested and is running at capacity and if nothing is done by 2037 congestion will be five times worse than it is today, constraining future development and growth opportunities.

The local air quality will also deteriorate further.

It is already operating at full capacity, with traffic queues and lengthy delays, resulting in longer and increasingly unreliable journey times for motorists.

Highways England initially unveiled three proposals to link the anti-clockwise M25 directly with the Chelmsford-bound A12 in 2016.

It eventually opted for an £80 million programme involving a looping cloverleaf link road scheme to connect the M25 at junction 28 with the A12, as well as providing local access to Brentwood via the A1023 Brook Street.