Extra capacity cannot be delivered along the main line between Norwich and Liverpool Street without major infrastructure upgrades, a report has revealed.

During the next two years, rail services on this route are expected to be transformed through the replacement of the entire fleet with new, higher capacity trains.

Network Rail says a degree of extra capacity can also be delivered through re-timetabling to fit in extra services.

But over the next 25 years the demand for rail transport in the high peak hour towards London Liverpool Street is expected to grow between 40 and 60 per cent.

Around 190 million journeys were made in 2017/18 within the East of England region compared to around 146 million in 2007/08, an increase of 30 per cent over 10 years.

Major improvements are needed along the route – notably at Bow, between Chelmsford and Witham, between Marks Tey and Colchester and at Haughley Junction near Stowmarket.

Without these upgrades Network Rail has said that extra capacity cannot be delivered.

This position has worried campaigners fighting proposals for major housing developments along the route – especially at West Tey which could see 24,000 homes as part of the North Essex Garden Community plans.

Rosie Pearson of the group Campaign Against Urban Sprawl (Cause), said: “We have been boring them to death for five years about rail capacity and asking how much they are going to collecting from developers.

“But Network Rail have ignored us at every opportunity and yet there are attempts to build a community settlement right next to the Great Eastern mainline.

“It is definitely not adequate and we don’t think they should be building a new town on an overcrowded line without investment in it first.”

The Network Rail Great Eastern Main Line Study published in July says the most significant capacity constraint is at Bow Junction, located between London Liverpool Street and Stratford.

It says this junction cannot accommodate any additional services in the peak hours beyond the current timetable, without a £100 million remodelling.

To deliver any additional services on the two-track section north of Shenfield, a combination of passing loops between Chelmsford and Witham and nearer Colchester is also needed.

A new station at Beaulieu may provide the infrastructure for a loop at Chelmsford, while at Marks Tey the Sudbury line platform could be used to allow for ‘main line’ northbound services to be held to allow faster trains to pass.

It is possible that some additional services can be achieved without these improvements by changing the timetable.

Doubling the junction rail layout at Haughley Junction could cost between £10 and £20 million and be delivered in the next three years, Network Rail has said.

But further actions include a timetable assessment of ‘trade offs’ in providing the additional fast Norwich service – followed by investigation of potential scope of the scheme.

Ms Pearson said: “There was a study in 2016 and that set out the very same list of what they called interventions – so they were looking at these then arguing we need those to cope with the increase demand on the line.

“It is obvious the rail network can’t increase capacity just with a few new trains and some timetabling and they do need to invest. At the moment that money is not coming from anywhere.

“This new report shows they still don’t have the money lined up and yet remarkably there are plans for 24,000 homes at Marks Tey and without development contribution to help pay for the improvements.”

The assessment has also indicated that further additional tracks may be needed between Shenfield and Chelmsford and between Ipswich and Haughley Junction.

However this need may be hampered if development near the railway increases the cost of provision of a four-track railway on these sections in the long term.

“The provision of headway improvements also provides an opportunity for increased capacity before more expensive schemes, such as additional tracks, are needed,” adds the report.

Reductions in headways can be delivered by an alteration in signal design, for example, by reducing the distance between signals.

The report has also reconfirmed the need to double the track at Trowse Bridge to achieve additional services to Cambridge and Ely in addition to services from London to Norwich before 2043.

A Network Rail spokesman said: “Our study sought to identify the expected growth on the Great Eastern Main Line over the next 25 years, additional services that might be needed and various infrastructural schemes required to run these.

“They include remodelling Bow junction, improving Haughey junction and creating train passing lines (“loops”) between Chelmsford/Witham and south of Colchester.

“We are still prioritising these schemes and conducting detailed timetable assessments that will allow public and private sector funders to make informed planning decisions.

“Therefore, the likely costs of each of these schemes cannot be determined at this stage.

“We are also developing the strategy in consultation with local councils and acknowledging the rising demands for housing in the area.”