I think you are expecting too much from the local elections. Looking at the councils website there are 4 Tory, 22 Labour, 21 Liberal and 2 independents councillors. The Liberals run the council at the moment but seeing that they have fewer councillors than Labour they must have the support of the independents.
I can’t see any party that takes control in May approving a massive new Luton Airport due to environmental reasons and the fact that the airport would be built on non-council land.
As owners of the airport Luton council seems to be in the unique position of actually being able to stop excessive expansion unlike the councils around Stansted who are fighting the government and the BAA who both see Stansted as the answer to London’s capacity requirements.