Heathrow should just go ahead and force the Government’s hand by submitting a full application for the third runway and associated works to the Planning Inspectorate. That should be dealt with fairly and independently with a recommendation being submitted to the Secretary of State. Remaining issues of land etc needn’t be sorted because you can submit an application on land you do not own.
Now, the SoS can go against the recommendation and there is no right to appeal. But if a refusal is unreasonable, ie because May, Johnson and a few other Tories *might* lose their seat, costs can be reclaimed. An awarding of costs along with the Inspectorate’s recommendation to approve would make an ongoing blockage of expansion untenable.