Air traffic controllers are increasingly complaining that safety could be compromised because they are too busy, figures reveal.

Staff at the main control centre in Swanwick, Hampshire, are making more than twice as many official complaints about their workload than this time last year, it has emerged.

The "overload reports" are completed whenever controllers think planes may have been put at risk because they were dealing with too many aircraft in too short a space of time.

Overload reports

Must be filed in any situation when controllers "experienced excessive workload to the point where safety is compromised" 30 filed so far this year 12 filed in the first five months of last year Nats says the reports do not indicate that safety actually has been compromised

National Air Traffic Services (Nats) said there have been 30 formal overload reports so far this year, compared to 12 in the first five months of last year.

But it denied safety was being eroded, saying there had been fewer actual incidents of near-misses since Swanwick opened in January.

Karl Schneider, the editor of Computer Weekly which first revealed the figures, told BBC Radio 4's Today programme the reports nevertheless indicated increasing potential for serious safety problems.

"This does show that the number of situations in which it's increasingly likely that those sort of near-misses occur, has gone up.

Staff are encouraged to report IT problems

"And you have to remember these controllers are already working under enormous pressure."

Nats chief executive Colin Chisholm denied that the overload reports indicated a problem with safety.

He said the main indicator of safety was the number of "airprox reports", where aircraft pass close to one another.

Since Swanwick opened, there have been none of the most serious Category A and B reports and only one Category C report - compared with seven in the same period in 2001.

'No safety risk'

"It's not the case that a mandatory occurrence report is filed when safety has been compromised," Mr Chisholm told Today.

"The definition is that it's a defect which 'has, or if not corrected, would have' compromised safety.

"In the case of overload reports, it's very clear that controllers file those when they feel the situation was busier than they're comfortable with."

The number of situations in which it's increasingly likely that... near-misses occur, has gone up

Computer Weekly editor Karl Schneider

He added that in the last five years, 160 overloads had been filed - but only five of those were actually associated with "loss of separation" (when one aircraft enters the protected space surrounding another).

He said controllers' difficulties were partly teething problems, with staff getting used to Swanwick and bedding-down its new computer system.

And managers had encouraged controllers to report any concerns, so adjustments could be made.

Tax-payers' cash

The �623m Swanwick centre, which controls most of the air space in England and Wales, has been dogged by problems since opening six years late in January.

It's not the case that a mandatory occurrence report is filed when safety has been compromised

Nats chief executive Colin Chisholm

It hit the headlines last month after planes were reportedly sent to the wrong airspace because controllers had difficulty reading the screens.

That came a week after thousands of passengers were left stranded at airport terminals when a computer failure caused chaos to flight schedules.

In the Commons earlier this week MPs heard that software changes to make the screens easier to read were not expected to be introduced until November.

They also heard the government was preparing to put a further �65m of taxpayers' money into the part-privatised Nats, to help it through a financial crisis engendered in part by a post-11 September slump in air travel.