London Heathrow, which was mentioned here, is solely restricted by runway capacity. They could increase capacity with mixed mode (using both runways for take of

London Heathrow, which was mentioned here, is solely restricted by runway capacity. They could increase capacity with mixed mode (using both runways for take off and departure) but the government doesn't allow that. Loosening the rules at Heathrow (mixed mode and removing restrictions for landings between 5am-6am) could easily boost capacity by 20-30%. I'm sure they'd find space for some more gates, part of the Terminal 1/2/3 area is unused anyway because of construction.