London mayor Boris Johnson reportedly believes the chance of a political deal for a second runway at Gatwick is fading.
This would leave attempts to solve the southeast aviation capacity crisis in potential deadlock.
Johnson has told friends that he thinks political splits will block expansion at Gatwick or Heathrow, regardless of the official recommendation due next year from the Airports Commission.
“I was told earlier there was this big political consensus emerging around Gatwick, but now I’m not sure it will happen,” Johnson is understood to have said, the London Evening Standard reported.
His remark will pile pressure on the Liberal Democrats to rethink their stance on airports.
Leader Nick Clegg planned to endorse Gatwick in a compromise designed to meet business demand for more flights, while continuing to oppose a third runway at Heathrow.
But this was blocked when Lib Dems staged a rebellion at the party conference in October and voted against any new runways in the south-east.
Business secretary Vince Cable, whose Twickenham constituency is on the Heathrow flight path, is said to be deeply unhappy with the vote, fearing it lacks credibility with business and could increase the likelihood of a third runway at Heathrow.
Johnson’s preferred option is a new four-runway hub airport in the Thames estuary, but that has been rejected as too costly by the Airports Commission.
The mayor then shifted behind Gatwick expansion as a temporary compromise.
Last month, the Standard revealed he had held private talks with Gatwick bosses, and in an interview with the Standard in July he described a second Gatwick runway as “a compromise”.
Johnson plans to campaign for his estuary hub if he is elected as a Conservative MP in May as expected.