New runways
I guess it all depends who sits in number 10 and with who's support.
Its worth remembering that Labour planned to go ahead with a new LHR runway had they been re-elected in 2010 given that its likely they (Labour) would require SNP support to Govern I can't see that the SNP would block a new runway at either LGW/LHR or both.
It would be more difficult for a Tory/Liberal alliance for sure.