Up to £650 million could be the final cost of improvements to Ely station and Ely North and to ensure continued access to the city for Queen Adelaide residents.

The figures were revealed in a report to the Cambridgeshire and Peterborough Combined Authority.

Last July the Department of Transport approved £200 million "as additional investment" to rail improvements for the Ely area that could be implemented by the end of 2024.

The report analyses the costs of providing extra trains to Norwich, Nottingham, Cambridge, Peterborough and March.

Paul Raynes, the combined authority's director of delivery and strategy, says there is capacity through the Ely area for 8.5 trains per hour at peak period and 6.5 trains per hour off peak.

"This is currently being fully utilised with 127 train movements per day," he says.

If 11 trains per hour operate hourly, with three of them freight, the bill for improvements would be £251 million on top of the £200 million already agreed.

But if the optimum 14 trains per day are provided then an additional £351 million would be required.

Ely needs the work, says the report, if the area is to cope with increasing demand for passenger and freight traffic.

Level crossing improvements, particularly at Queen Adelaide and Kiln Lane, remain urgent. Speed limits as low as 20mph are in place for some parts of the Ely area, says the report.

Another objective of the combined authority is to enable additional stopping services at Whittlesey, March and Manea.

And £96.5 million will be required for work at road and rail crossings at Queen Adelaide.

"Significant investment is required on improving the line between Peterborough and Cambridge to truly unlock the benefits and to maximise the 11 to 14 trains per hour," the report concludes.

Between March and Cambridge there are 39 level crossings, says a separate report by consultants Mott MacDonald, and each will need risk assessments.

"Any additional services running through the existing level crossings between March and Cambridge would increase level crossing risk and could trigger a requirement to upgrade these level crossings (e.g. replace with bridges)," Mott MacDonald conclude.

A task force of interested parties from across Cambridgeshire and Norfolk is to send a letter to local MPs to lobby government "to ensure the programme is maintained and where possible accelerated".