Further changes could be made to the controversial plans for the high-speed HS2 rail network, Transport Secretary Patrick McLoughlin has indicated as the Government launched a "fightback" over the £42.6 billion scheme.
Mr McLoughlin promised to "squeeze every penny" of economic benefit out of the project as a new analysis concluded it would be worth £15 billion a year by 2037.
He said he it would be "absurd" to claim the scheme was perfect and ministers promised to "adapt and improve" the plans in response to criticism of the project, which will create a high-speed link between London and cities in the Midlands and northern England.
MPs on the Commons spending watchdog issued a scathing report on the scheme this week, warning that the apparent benefits were dwindling as the costs soared.
The case for the massive project was based on "fragile numbers, out-of-date data and assumptions which do not reflect real life", with no evidence that it would aid regional economies rather than sucking even more activity into London, according to the Public Accounts Committee report.
The scheme has also faced opposition from a number of Tory MPs, with seats in Conservative heartlands lying along the proposed route. The persistent criticism led David Cameron to launch a campaign to bolster support for the scheme, which the Government claims will reduce the north-south divide and help the UK compete.
The Prime Minister said "the fightback begins on HS2" with Mr McLoughlin's speech, which said the increased capacity offered by HS2, rather than reduced journey times, were the main benefit.
Making a case for the scheme in a keynote speech in Westminster, Mr McLoughlin said all major infrastructure projects were controversial. He said: "The last few weeks have seen old criticisms return in new guises. About cost. About capacity. About the balance between north and south. And I don't dismiss all such criticism. Some of it is well-meant. Some of it is well-informed. Some of it is ill-informed and deliberately misleading.
"All of it deserves - at the very least - to be listened to respectfully. So where we can adapt and improve our plans my promise is that we will. The new north-south railway is a project that will last over decades and no doubt over several governments too. We are still consulting. Parliament will have its say. It would be absurd to claim we have got every bit right."
The new analysis by accountants KPMG concludes that productivity gains to the West Midlands as a result of HS2 will be worth between £1.5 billion and £3.1 billion a year by 2037. In Greater Manchester the benefits will be worth up to £1.3 billion and up to £2.2 billion in the East Midlands.