The rising cost of the Croxley Rail Link has forced the government to step in and ask a rail provider to take on an "enhanced role" in the construction of the project.

London Underground said the government has asked them to take on the role in delivering the project after the estimated cost rose by £110 million.

The Croxley Rail Link is now expected to cost £230 million and the county council said "minimal work" would be needed to run services from Watford to Amersham.

Hertfordshire County Council and London Underground are discussing who will be responsible for specific aspects of the project, but they could take over construction of the project next year, though the rail provider stressed no decision has been made yet.

David Hughes, director of major programme sponsorship at London Underground, said: "The Croxley Rail link is a Hertfordshire County Council led project.  Due to increases in the cost estimates for the project, London Underground has been asked by the Government to consider taking on an enhanced role to deliver the project.  

"No decisions on this have been taken and to suggest that the cost of the project has increased because of our involvement, or because of our suggested choice of technology, is simply incorrect."

County council officials attributed the higher price of the project to 'wider railway benefits' and the cost of inflation. The scheme had been expected to cost in the region of £120 million.

Jo Brown, from Hertfordshire County Council, said: "The wider railway benefits include refurbishing the existing line between Lower High Street and Watford Junction, as well as enhancing the power supplies to both the Metropolitan Line and the Network Rail sections.

"The improvements being made will allow more trains to run in the future, not just on the Croxley Rail Link but on the wider train network.  

"In addition, while the Croxley Rail Link will not immediately enable services to run from Amersham into Watford Junction, it has been designed so that this can happen in the future with minimal work."

Construction has been put back until Spring after it was scheduled to start earlier this year and organisers  hope trains will start running in Spring 2018. 

Dorothy Thornhill, Watford’s Elected Mayor, described the rail link as "absolutely critical to unlocking Watford’s future economic potential".

The Liberal Democrat prospective parliamentary candidate said: "The Croxley Rail Link is a transformational project for the town.

"It is the thread that links Watford’s major development projects together - Watford Health Campus, Ascot Road, Watford Business Park, Watford Junction Interchange and Charter Place Shopping Centre. 

"That’s over £1.2 billion of investment to the benefit of our residents and businesses." 

The scheme will see the Metropolitan Line routed from Croxley Station, to a new one in Ascot Road called Cassiobridge, then another new station in Vicarage Road called Watford Vicarage Road before 
connecting with Watford High Street Station and then terminating at Watford Junction.

As a result of the scheme, Watford Metropolitan Station will close to passengers and be used as siding.

Terry Douris, Cabinet Member for Highways, said: "We have been working very hard to deliver this vital railway development for Hertfordshire, which will have so many benefits for the area. 

"We are now in discussions with London Underground about their potential greater involvement, given that they will ultimately own and operate the railway. I would like to thank everyone involved in getting the project to this stage."