Dan Hawkes, head of avionic systems at the Civil Aviation Authority (CAA), cites a typical incident.

The BBC's Hugh Sykes talks to pilots about their concerns

"A go-around was initiated by the flight crew - that is, he aborted the landing, because of interference from a mobile phone.

"He heard the interference in his headphones, and at the same time his automatic landing system was showing anomalous behaviour. He decided it was unsafe to continue with the automatic approach."

In another incident, the stick-shaker in the cockpit, a warning signal that the plane is about to stall, started to operate. The plane was on the ground at the time. A passenger at the back was found to be using a mobile phone.

Anecdotal evidence

But most of the evidence is circumstantial and anecdotal. There is no absolute proof mobile phones are hazardous. But, as Mr Hawkes explains, even the possibility of interference by mobile phones has serious consequences.

"There's an industry consensus, throughout the world, that mobile phones are a potential hazard to aircraft and must be switched off.

Mobile phones give out signals continuously while they are switched on

"A typical aircraft these days could have anything up to 15 or more radio systems on board. The signals that a mobile phone gives out could penetrate into equipment, and could affect the operation of the computer.

"The computer may shut down, which would affect the aircraft's navigation, which in turn would affect the signals sent to the auto pilot, and the way the aircraft is automatically flown.

"The aircraft might go off course, and even might change height."

Carolyn Hawkins, who advises on safety for the pilots' union, Balpa, says absolute proof is not needed.

"If you've got navigational systems being affected, by whatever it is being affected by, and you turn off the mobile phones, the laptop, the CD player, whatever, and it corrects it - let's stick with that, let's be safe in the air."

Grave risk

Part of the problem is that mobile phones emit signals even when they are not being used, if users leave them switched on. They are hunting for their nearest ground station to make a connection.

Safety in the air is paramount

The CAA has decided the chance such signals may interfere with the complicated electronic systems, now largely relied on by pilots, is too grave a risk to take.

David Learmount, of Flight International, agrees. "As a result of all this anecdotal evidence which they haven't been able to prove, they are justifiably nervous. It is a serious matter.

"Although it has not been proven that these machines can make aeroplanes go off course, they really don't want to prove it."

It may be that mobile phones are not hazardous to all aircraft.

'Older models more vulnerable'

Neil Whitehouse, found guilty in June of endangering an aircraft because he refused to switch off his mobile phone, was on board an older model.

Mr Learmount says: "This fellow happened to be using his mobile phone on board a Boeing 737.

"The 737 was designed in the early 1960s, and that aeroplane has never had its electronic equipment screened against the kind of emissions that mobile phones put out.

"Whereas in the more modern aeroplanes, like the fly-by-wire, computer controlled Airbus A-320s, A330s, A340s, they have been screened.

"So he could actually say if this aeroplane had been an Airbus he might well have walked away from the court."

But even if you use a mobile phone on an aircraft which has been screened, it is still against the Wireless and Telegraphy Act.

That will be a great relief for people to whom aeroplanes are about the last place left where you can eat, sleep, think and relax without being disturbed by electronic warbling.