Business groups have jumped on data showing Gatwick recorded its busiest ever month in its 80 year history to push for a decision on aviation capacity.
Some 4.6m passengers travelled through the airport in July, up 6.9 per cent on the same month last year, while long-haul jumped 23 per cent.
Business groups welcomed the news, but indicated it highlighted to failure of government on the long-awaited decision of where to expand aviation capacity in the south east.
London Chamber of Commerce and Industry chief executive Colin Stanbridge said: "It’s great to see our main airports are busier than ever but in order to future-proof the UK economy we need to increase airport capacity to serve the capital and the rest of the country as soon as possible.
"London businesses have repeatedly called for a decision on a new London runway. The government has long had the information it needs to make a decision, yet continues to delay."
Meanwhile, David Leam, infrastructure director at London First, said: "These figures send a powerful signal that Britain remains open to the world. But for London to continue growing as a global centre of trade and tourism, ministers must in the coming weeks give their backing to the new runway capacity our economy so badly needs."
Dan Lewis, senior infrastructure policy adviser at the Institute of Directors (IoD): "Expanding airport capacity should be at the top of the new Transport Secretary’s list for actions to boost business confidence. IoD members see advantages to both Heathrow and Gatwick as locations for a new runway, but the key thing is getting a conclusive decision that leads to a rapidly completed runway."
Gatwick itself said the figures show the case for a second runway is mounting. Chief executive Stewart Wingate said: "Gatwick’s continued long-haul growth and strong cargo growth are the latest proof that competition in the London airports’ market is working. Our continued success provides proof of the benefits a two runway Gatwick would deliver for Britain. Expansion of Gatwick, London’s fastest growing long-haul gateway, would show London is open for business to the world."
However, figures released last week based on UKTrade Info and HMRC Data shows that 29 per cent of all non-EU exports were transported via Heathrow, compared to just 0.2 per cent at Gatwick.
And, further indicating the role of Heathrow as a hub, the data showed Heathrow cargo value has been growing strongly by an average of 9.5 per cent between 2010 and 2015, while Gatwick’s has been declining by 4.3 per cent over the same period.
A Heathrow spokesperson said: "July was a fantastic month for Heathrow – our world-class terminals and hard-working colleagues welcomed a record 7.44m passengers, the most in a single month in our 70-year history.
"And just as more passengers were flowing through the doors of our terminals, cargo volumes at the UK’s largest port grew a healthy 2.6 per cent – meaning more of Britain’s exports were flying in the bellyholds of aircraft on their way to customers around the world.
"The Prime Minister is committed to securing Britain’s legacy as an outward-looking trading nation and an expanded Heathrow will help her do it."
The news comes after it was announced in June that the airport expansion decision has been pushed back until "at least" October.
Business leaders have been pushing for a quick decision since the Davies Commission was published last July, recommended building a third runway at Heathrow.
The government said in December it would delay making a decision on airport expansion in the south east until at least this summer, saying "more work will be done on environmental impacts" in the interim.
Philip Hammond, the newly-appointed chancellor, has said that a decision should be taken soon after Dubai surpassed Heathrow as the world's busiest airport.