Britain's troubled air traffic control service has admitted travellers face more delays next year because of controller shortages and computer problems.

The recently part-privatised National Air Traffic Services (Nats) said it would again be understaffed during the 2003 summer holidays, but not by 30 to 40 controllers it lacked this year.

"On our current estimates, we would think (we will be) up to 12 controllers short next summer, " Nats chief executive Richard Everitt told a parliamentary committee.

The government sold-off 46% of Nats last year to a consortium of airlines - known as the Airline Group - which includes British Airways, Virgin Atlantic, easyJet British Midland.

Sale defended

The sale reversed Labour party policy which opposed the privatisation while in opposition.

The crisis at Nats, which earns money from aircraft flying through British air space, was intensified by the 11 September attacks on the US and the resulting slump in air travel.

The Department of Transport and Industry defended the Nats privatisation.

"The honest truth is that in the circumstances at the time the world looked a less risky place than it was after September 11," the department's permanent secretary, Rachel Lomax, told the committee.

Upgrade delay

The company earns almost half its revenues on transatlantic routes.

Computer problems at its control centre grounded air travel several times this year and the company admitted the financial troubles meant it would could not fund faster modernisation.

"It does remain one of our vulnerabilities," said Mr Everitt.

He said the air traffic control computer software, which has brought traffic to a stand-still at times, could still be in use in 10 years time.

The software dates back to 1975.

Nats investment to upgrade the system �50m this year from �64m in 2001.

The British aviation industry regulator last month loosened the contractual requirements for Nats to lower fees for airlines, clearing the way for a �130m government bail-out.