Heathrow airport had its busiest ever month for passengers in July, but airports outside London suffered flat or falling traffic.

The airport operator BAA said a whopping 6.71 million passengers passed through Heathrow in July, a 3.5 per cent jump on the same month last year.

The UK's biggest airport was helped by an end to the Icelandic volcanic ash disruption and a temporary cessation in industrial action by British Airways cabin crew.

A further boost to Heathrow came from continued strong traffic from overseas visitors and the fact that it remains a crucial transfer hub for long-haul flights that start outside the UK.

The main source of passenger growth at the London airport was the European market, where additional capacity drove an increase of 9.5 per cent. It also benefited from strong demand from Brazil, Russia, China and India.

"Heathrow is definitely more resilient because of the hub nature of the airport for passengers who use London to transfer to other destinations," a BAA spokesman said.

"We have been saying for a while that we would have had good figures if had not been for the volcanic ash or BA industrial action." However, he warned: "We are not yet out of the woods."

Industry sources also suggested that Heathrow is benefiting from a stronger recovery in London's economy, given that business passengers account for about one-third of its traffic.

In contrast, the reliance of Stansted on low-cost airlines suggests this was behind a 7.2 per cent slump in passengers numbers to 2.02 million in July.

In fact, Stansted was the worst performing of all the UK airports. Aberdeen airport suffered a 4.1 per cent slump in passengers to 276.9 million last month, which was slightly worse than 3.6 per cent fall at Glasgow. Meanwhile, passenger numbers rose marginally by 0.6 per cent at Edinburgh.

Total UK passenger numbers came in higher by 0.3 per cent at 10.95m in July.