UK investment in high-speed rail networks could provide a bigger boost to the environment and economy than a third runway at Heathrow airport.
A report from the Campaign for Better Transport says high-speed rail links have the potential to create thousands of jobs for Britain and render expansion at Heathrow unnecessary.
The study Who says there is no alternative? was commissioned by the Rail and Maritime Transport union (RMT) and notes a third of flights at Heathrow are to short-haul destinations better served by rail.
RMT general secretary Bob Crow told the union's annual conference in Nottingham high-speed rail could create a "win-win" solution for the economy and environment.
"Paris remains Heathrow's top destination and there are as many flights leaving for Edinburgh as for New York, and if we provide a viable, fast and sustainable alternative to short-haul flights the case for Heathrow expansion would evaporate," he claimed.
"Our report underlines the urgency of the review announced by Network Rail and for the government to ensure that it acts swiftly to reap the clear environmental and economic benefits that high-speed rail can bring."
Labour MP John McDonnell, whose constituency of Hayes and Harlington includes Heathrow, added: "This report proves conclusively that there is a rail alternative to Heathrow expansion and undermines totally the argument for a new runway and sixth terminal.
"It should provide the basis upon which the government thinks again."
Mr McDonnell is also chair of the RMT's parliamentary group.