Half-hourly trains from King's Lynn to London could be made a condition of the new franchise to run services on the Fen Line, it emerged tonight.

That means whoever ends up running trains on the route, after First Capital Connect's franchise ends next September, could foot the �25m bill for work needed at Ely North junction.

Transport Secretary Justine Greening said both options were being considered, when she met South West Norfolk MP Elizabeth Truss and Mid Norfolk MP George Freeman, who have been pressing for improvements on the line.

After the meeting Ms Truss said: 'It was a very positive meeting and she said it was very timely as she was looking at network rail's investment programme.

'We want the half-hourly service to be specified in the franchise, we want to get there by hook or by crook.'

Improvements at Ely North would allow trains to run half-hourly between King's Lynn and King's Cross, easing over-crowding on the main route between the Fens and the capital.

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 link line which allows direct services between Norwich and Peterborough to by-pass Ely station.

MPs have already given the government a cost - benefit analysis for the cost of improving the layout of the junction, showing services between Norwich and Cambridge and Norwich and Peterborough would also benefit from the work.

After a rail summit organised by Ms Truss in January, transport minister Theresa Villiers said the scheme was something the government was 'looking at carefully'. She said the department of transport had asked Network Rail to look in more detail at the proposals.

First Capital Connect's franchise to run services 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.

Tendering is now under way for the contract, which a Department for Transport briefing paper says was worth �1,010m in revenue in 2010/11.

The number of journeys made on the Fen Line is increasing. Downham Market station alone has seen a 64pc rise in passenger numbers - an extra 160,000 a year - since 2002.

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