The architect of plans for a new high speed rail line has urged Birmingham and the West Midlands to demand the project goes ahead as he warned that Ministers were “losing their nerve”.

Former Transport Secretary Lord Adonis accused the Government of giving in to “Nimbys in the Chilterns” after Ministers announced they were delaying a decision on the planned high speed rail network linking Birmingham to London and the north.

Justine Greening, the Transport Secretary, scrapped plans to make an announcement before Christmas about the findings of a five-month consultation into plans for the £17 billion line, known as HS2.

She revealed that she was delaying a decision until the new year, following a heated meeting with MPs in which senior Tories demanded radical changes to the proposals.

West Midland MPs Michael Fabricant (Con Lichfield) and Jeremy Wright (Con Kenilworth and Southam), both Conservative whips, urged the Government to develop a service much slower than the planned 225mph line.

Under the HS2 proposals services would initially run at 225mph and speeds would eventually increase to 250mph – but Mr Fabricant said trains should run at just 180mph, which would allow a new route to be drawn up following existing transport corridors.

Sources inside the Government insisted the delay did not mean the project was under threat and pointed out that Prime Minister David Cameron had personally backed high speed rail on many occasions.

Labour peer Lord Adonis was an outspoken supporter of high speed rail in his role as Transport Secretary. He committed the Labour government to building the line in March last year, when he set out plans for a Y-shaped network with a single line from London to Birmingham which then splits into two lines to Manchester and Leeds.

Speaking to the Birmingham Post, Lord Adonis: “It looks as if Justine Greening has suffered a severe loss of nerve in the face of opposition. Birmingham and the West Midlands need to say loud and clear that their interests are at stake and this essential project must not be derailed by a group of Nimbys in the Chilterns, which is what appears to be happening.”

A Whitehall source said Ms Greening’s decision to make an announcement in January would not hold up the project by more than a couple of days.

Parliament needs to approve a “hybrid bill” authorising construction of the line, but this is not due to come before the Commons before 2013. Ms Greening has delayed the announcement so that officials can consider whether it would be possible to reduce the environmental impact of the line by building a 1.5-mile tunnel beneath the Chiltern Hills, which would connect two tunnels already in the plans, at a reported cost of £500 million.

However, she revealed very little in her statement to the Commons, saying only: “In order to ensure that my decision is based on a careful consideration of all relevant factors, I have concluded that I should allow myself until early in 2012 to announce my decisions.”

High-profile opponents of the scheme within the Government include include Welsh Secretary Cheryl Gillan, who has reportedly threatened to resign if it goes ahead, and Dominic Grieve, the Attorney General. Both MPs represent seats in Buckinghamshire.

Birmingham MP Gisela Stuart (Lab Edgbaston), Secretary of All-Party Parliamentary Group for High Speed Rail, condemned the delay and urged David Cameron to take charge of the project.

She said: “There is no other reason for the delay other than internal politics.

“A project like this needs to have momentum. They are giving out the wrong signal. The Prime Minister needs to make up his mind whether he is in charge or not.”

But fellow Birmingham MP Roger Godsiff (Lab Hall Green), who opposes the scheme, said: “I’m pleased the Government is delaying making a decision and is looking again at the facts.

“I hope the new Minister will come to the conclusion that spending £17 billion on getting people from London to Birmingham half an hour quicker is not a good use of public money when we are supposed to be living in austerity.”

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