Eurocontrol, the European Organisation for the Safety of Air Navigation, said about half of flights travelling across Europe could be subject to delays after a system failure at about midday on Tuesday.

The organisation said that its “enhanced tactical flow management system” had failed. The system links to air traffic control centres across Europe to determine when flights can best take off or land, affecting flight planning.

About half of the 29,500 flights expected to operate on Tuesday in the European network could be delayed, it said.

A significant proportion of flights in and out of London City airport were delayed, although Heathrow said it had been largely unaffected.

Work to restore the system was under way after the problem was identified, but it was unlikely to be in operation before the evening.

Air traffic control systems are being increasingly interlinked in the development of the Single European Sky, which the aviation industry hopes will increase the efficiency of flights and make best use of airspace.

More disruption could be in store for air passengers in the UK from Wednesday as the Nats air traffic control centre at Swanwick, which manages the airspace handling most British flights, continues the digitisation of its systems.

Passengers face potential delays as airspace capacity is reduced during the transition period, when the use of paper flight strips to document instructions to pilots from controllers is phased out in favour of an electronic system.

While Nats has started the process, this week will be “undoubtedly the most challenging”, according to Pete Dawson, the general manager of Nats’ LondonTerminal Control, as it affects airspace covering Britain’s biggest airports.

Nats has warned that delays of up to 20 minutes for some flights are possible at peak times, and that flights may have to operate later at night and earlier in the morning at Heathrow and Gatwick during the transition.

The move comes as part of a broader overhaul of airspace, which controllers and the Department for Transport want to see modernised and reshaped to provide more capacity, with the skies increasingly congested in the south-east of England.

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