Air traffic controllers are dealing with the busiest day in UK aviation history.
A total of 8,800 planes are to be handled by controllers across the country over 24 hours, with flight numbers reaching a peak between 6am-8am and 4pm-7pm.
Some 770,000 flights are expected in UK airspace over the summer - 40,000 more than last year.
Jamie Hutchison, director of Nats' air traffic control base in Swanwick, Hampshire, warned that the "ageing design of UK airspace" means the country is reaching the limit of how many flights it can accommodate.
A UK-wide forecast from the Department for Transport warns that if airspace remains unchanged, by 2030 delays could be 50 times worse than they were in 2015.
A Government consultation could result in changes to permitted routes to allow more flights, Nats said, and the system could be updated to take advantage of the ability of modern jets to fly further and take steeper approaches to airports, to maximise the use of available space while minimising noise disruption and pollution on the ground.
But redesigning flight paths is a contentious issue as it can mean communities currently unaffected by aircraft noise are put under flight paths.
The record day came as the Government launched its proposed aviation strategy for the years to 2050, in which ministers say they are "minded to be supportive" of airports that want to make "better use" of existing capacity.
Mr Hutchison said the busy day at airports has not taken controllers by surprise.
"We work very closely with our airline and airport customers in the run-up to the summer to ensure we have the right planning and resources in place to get people away safely for a well-earned holiday," he said.
"It's our busiest time of year and traffic growth is outpacing forecasts year-on-year.
"In the last few weeks we have already safely managed record-breaking daily traffic levels, but the ageing design of UK airspace means we will soon reach the limits of what can be managed without delays rising significantly."
Proposals included in the Government's aviation strategy include doorstep luggage collection services and town centre check-in desks for passengers flying from British airports.
The scheme - already in use in Hong Kong and Japan - would allow travellers to have bags collected from their homes or to drop their bags at a depot in advance and pick up boarding cards before making their own way to the airport, making life easier for disabled passengers and saving space on commuter trains currently taken up by luggage.
Also under consideration are extra measures to deal with the terror threat, including funding for better airport security in foreign countries that have weaker systems.
The Government also raised the prospect of reforming Air Passenger Duty to improve the competitiveness of British airports.
Transport Secretary Chris Grayling said: "Our new aviation strategy will look beyond the new runway at Heathrow and sets out a comprehensive long-term plan for UK aviation.
"It will support jobs and economic growth across the whole of the UK."
It comes as a £1 billion programme to double the size of Manchester Airport's Terminal 2 was launched.
The investment was described by the chief executive of Manchester Airports Group, Charlie Cornish, as "a significant moment" which demonstrated "the confidence that we have in the long-term future of both the North and the UK economy".