Transport secretary Justine Greening was last night urged to give the green light for work to revamp a railway 'bottleneck' and boost Norfolk's economy.

South West Norfolk MP Elizabeth Truss and Mid Norfolk MP George Freeman have been pressing for improvements at Ely North junction which would allow trains to run more frequently between King's Lynn and London, as well as Norwich and Cambridge.

It came as the Department of Transport confirmed the �25m improvement work was one of the projects being considered for the next round of investment to be announced in July.

Ms Truss said: 'For a small investment, in railway terms, the improvement work at Ely North would spark a huge amount of growth both along the Fen Line and the Norwich/Cambridge line, and help drive a lot of business to the area.

'We have reached a critical point where the Department of Transport needs to make decisions before franchise agreements are made and we feel the improvement work is urgently needed.

'The government is keen to support projects which will boost growth and this is a classic example of that.'

Improvements at Ely North would allow trains to run half-hourly between King's Lynn and London and the work could be made a condition of the new franchise to run services on the Fen Line.

The junction, on the outskirts of the city at Queen Adelaide, is a key cross-over for north-south and east-west rail routes across the region.

There are three level crossings within yards of each other, where lines to Peterborough, King's Lynn and Norwich meet, along with a line which allows direct services between Norwich and Peterborough to bypass Ely station.

MPs have already given the government a cost-benefit analysis for the �25m needed to improve the layout of the junction, showing services between Norwich and both Cambridge and Peterborough would also benefit from the work.

Ms Greening has previously said the Department for Transport was looking to 'even out' rail spending across the country.

Norfolk's MPs have also made the point that investment in the county has lagged behind that made in other areas.

Investment in the east-west rail infrastructure would also help to maximise the benefits of last week's government money for scientific research and development in Norwich and Cambridge.

Norwich Research Park (NRP) received �90m of a �250m pot to boost work on life sciences – the study of food science, biomedecine and energy – at the John Innes Centre, Institute of Food Research and Genome Analysis Centre in what was described as a 'massive vote of confidence' in NRP and its vision to attract companies to the edge-of-Norwich campus.

Mr Freeman said last night: 'Last week saw the announcement of more than �150m government support for scientific research in Norwich and Cambridge.

'The Cambridge/Norwich clusters and the A11 innovation corridor linking them is fast becoming recognised as a world-class engine of new technologies, businesses and markets but we can't build a 21st century economy on 19th century infrastructure.

'The upgrade of the Ely North Junction bottleneck is pivotal to both improving commuter links and opening up fast links between Cambridge and Norwich which we know are vital to investment and business creation.'

MPs from across East Anglia are currently working together on a rail manifesto for the Eastern Network, which they will be presenting to the transport secretary before the summer.

First Capital Connect's franchise to run services between King's Lynn and London ends in September 2013. From then services on the Fen Line will become part of the new Thameslink franchise, which will also include some routes through and south of London.

Campaigners say more trains, longer platforms and bigger car parks are needed to meet growing demand on the line, Norfolk's fastest rail link to the capital.