By Theo Leggett, BBC News
After years of discussion and delay, the government is due to decide this week whether to build a new runway at Heathrow Airport, or at Gatwick.
But given that Heathrow is already operating at maximum capacity, and its rival is expected to run out of space within the next few years, why does it have to be one option or another?
Put simply, why hasn’t the option of building an additional runway at both Gatwick and Heathrow been seriously considered?
Environmental constraints, public opposition and economic arguments all come into it, but the simple answer appears to be: politics