A new report says the HS2 rail project could boost the UK economy by £15bn a year.
Transport Secretary Patrick McLoughlin presented the findings as he re-asserted the case for the new rail line.
The report, from accountants KPMG, says that regions outside London will be the biggest beneficiaries of the new service.
But the economic boost would not be felt until 2037, the report said.
John Longworth, director general of the British Chambers of Commerce, told the BBC: "Businesses up and down the country are absolutely convinced that this is a really important infrastructure project. It is one of the key infrastructure projects for the UK."
He argued that simply renovating existing rail lines that were "creaking at the seams" would cause "chaos".
In response, Mark Littlewood, director general of the Institute of Economic Affairs, said: "Any private investor would consider this to be a colossal waste of money.
"That is not to say that we don't need to improve capacity. Rail is an extraordinarily expensive way of doing that."
The government was asking UK taxpayers to take "a huge gamble on their extremely dodgy numbers", he added.