They said they were "absolutely determined" to scrap the projects if they win the next election. The warning came in the same week that Stansted airport got the go ahead to increase its capacity from 241,000 to 264,000 flights a year.
Shadow transport secretary Theresa Villiers was adamant that her party would halt these plans. "We will not consider ourselves bound by any decision taken by this government (on Heathrow). People involved with contracts should be warned - we will stop a third runway going ahead."
The decision to increase capacity at Stansted was the first major decision to be made by new transport secretary Geoff Hoon since Gordon Brown’s reshuffle last month.
It will result in an increase in the maximum number of passengers using the airport from 25M to 35M per annum. This equates to around 120 flights a day.
Expansion is expected to pave the way for a second runway at Stansted. A public inquiry into this is due to start in April 2009. Airport expansion plans across England had mixed fortunes last week. The London Borough of Newham gave London City airport the go ahead to expand the number of flights it handles by 50%. But Coventry Airport has had its appeal against the rejection of plans to build a new passenger terminal overturned by a High Court judge.
The airport had challenged the government’s decision to block the expansion, which would have doubled passenger numbers to 2M each year.