Disruptive passenger forces Qantas flight QF2 from London to Dubai to make a U-turn

QANTAS staff turned to passengers for medical help as an unruly flyer forced a flight to turn back to London.

The crew was about to serve dinner, about an hour into flight QF2 to Dubai, when the disruptive passenger's threatening behaviour forced them to turn back to London.

The crew restrained the passenger on board the Qantas A380 and the flight was met by local authorities on its return to Heathrow.

A Metropolitan Police spokesman told News Corp police had detained a 40-year-old British man.

It took six flight staff to restrain the man, who was seated on the upper deck of the plane, another passenger on board the flight has told News Corp.

Passengers on board said the crew asked any doctors or nurses to come forward to assist, and police boarded the plane to take statements.

Qantas did not give any further details about the incident.

"This type of disruption inconveniences our customers and comes at significant cost to Qantas, but we take a zero tolerance approach to aggressive behaviour on board," the airline said in a statement.

The flight, which was originally scheduled to depart London at 9.15pm local time, landed back in London just before midnight (11am AEDT).

It flew out a second time more than two hours later, about 2.20am local time (1.20pm AEDT).

Melbourne-bound Gemma Prata, who contacted News Corp while waiting for the plane to take off again, said: "Qantas staff are handling it well, giving us regular updates."

She said many passengers were unaware of the commotion until the flight was turned back.

"The passenger is on the upper deck, so those of us on the lower deck were unaware of what was going on until the cabin crew filled us in," she said.

"They were asking if there were any medical doctors or trained nurses on board willing to help out.

"It happened just as they were about to serve dinner.

"At the moment police are taking statements and we are waiting to hear what will happen next, but the crew are handling it well, providing us with refreshments and keeping us updated whenever they hear anything."

Passengers Lee, Elizabeth, Michael and Rebecca also emailed News Corp to share their experience.

"The staff is absolutely fantastic," they wrote.

"We are a bit hungry. A glass of Shiraz would go down a great but unfortunately they have locked the bar due to regulations lol."

Meanwhile, Lawrie Platt posted on Twitter: "Brilliant. Been on the plane for 4 hours and only got to Germany and back ..."

He added: "This is a bit of a nightmare! Just seen the 'passenger' get off though ... didn't get a great look but 30-35 years old. Short, slightly rotund, went straight into the ambulance."

Qantas said it was working to ensure the aircraft departed London again as soon as possible.

The delayed flight is now expected to arrive in Dubai at 11.30am local time, before it continues to Sydney.

Flight tracking site Flight Radar 24 showed the plane take a U-turn near Frankfurt, Germany.

Concerned son-in-law, Andrew Lee, posted on Twitter: "motherinlaws first flight for 20 years travelling alone to visit us in Sydney - turned back to London? #fail #stressful"

The mid-flight drama comes just days after the embattled airline announced it would becutting 1000 staff in a bid to save $2 billion over three years.

Qantas last week announced plans to cut at least 1000 staff as it revealed a before-tax loss of $300 million for the first half of the 2013-14 financial year.