The white middle-classes gathered in Parliament Square to protest against plans for a third runway at Heathrow airport - blighting, they say, thousands of homes in London's aviation hub's flight paths - especially to the west of the capital. Central to the demonstration were both London mayoral candidates: the Conservative Zac Goldsmith and Labour's Sadique Khan. The £17bn expansion at Heathrow would mean 250,000 more flights a year.