LONDON—Prime Minister David Cameron says Britain will hold an inquiry on the capacity of its stretched airports amid a debate over the merits of expanding London’s Heathrow Airport.

Cameron told legislators Wednesday he would shortly announce the details of a review that will involve all major political parties.

Heathrow—Europe’s busiest airport—is operating at capacity with 1,300 landings and takeoffs every day. Some business groups fear an inability to add flights will dent Britain’s competitiveness.

Cameron said he would stand by his government’s pledge not to build a third runway at Heathrow before the 2015 national election.

But analysts see the inquiry, and Cameron’s decision Tuesday to replace the transportation secretary who opposed a third runway, as setting the stage for a policy change after the election.