Theresa May is already being challenged by several west London-based Tory MPs ready to oppose a third runway and may have to rely on votes from the SNP and DUP to get it through the Commons in the coming weeks.
The decision to press ahead with expansion of the airport was announced on Tuesday after years of wrangling and delay.
After Prime Minister’s Questions, a senior Labour source said the party was “sceptical” over whether the Government’s plans for Heathrow would meet its four tests for airport expansion in the South-East, revolving around capacity, noise, the environment and regional connectivity.
The source said Labour would have to examine full details of the proposals before deciding whether its MPs should vote for the third runway plans, but added: “It has to meet those four tests. So far, what we have seen looks like the existing proposals don’t do that.”
Ministers also faced a potential backlash from northern MPs after a Commons committee’s analysis of official projections showed Leeds Bradford Airport would see 4,449 fewer international flights a year by 2030 if expansion went ahead.
Doncaster Sheffield Airport would lose 1,413 while the North’s major hub - Manchester - would lose 20,258.
Keighley MP John Grogan, who requested the figures from the Commons Transport Committee, said Heathrow expansion would mean Britain’s regions losing out.
The Labour MP also questioned the Government’s pledge to ringfence 15 per cent of slots on the new runway for domestic connections to the rest of the UK.
Mr Grogan told The Yorkshire Post: “These official figures clearly illustrate that Heathrow expansion will be at the cost of international flights to and from the other nations of the United Kingdom and English regions outside London and the South East.
“More direct point to point international flights from the North are what is needed for growth.
“Ministers have offered no practical support for this.
“Furthermore empty promises of connections to Heathrow are worth little more than the paper they are written on as recent cuts in flights from Leeds Bradford to Heathrow indicate.
“Frequent connections to Amsterdam from airports like Leeds Bradford in the North are now more important for onward connections than the handful of flights to Heathrow.”
Doncaster Sheffield Airport said there were “many variables” in the Department for Transport (DfT) forecasts which it said primarily focuses on national rather than regional demand.
“Overall passenger demand for the UK will continue to increase and we feel that at DSA we are well placed to accommodate it.”
A DfT spokeswoman said overall passenger numbers would rise with the 15 per cent ringfence.
She said: “Our analysis shows that regional airports will continue to grow strongly with expansion at Heathrow and passenger numbers are expected to see an 80 per cent increase by 2050.”