Heathrow Airport
Passengers line up in Terminal Three as they wait for delayed flights at Heathrow AirportGetty

Thousands of travellers due to fly from British airports have been left stranded after flights all over Europe have been cancelled ahead of a planned strike by French air traffic controllers.

Hundreds of flights have been grounded, while many more were disrupted, with delays affecting flights to and from France as well journeys to other parts of Europe accessible through French airspace.

France's largest union, the SNCTA, called the strike on Wednesday 8 May and Thursday 9 May in a dispute over increasing the pension age.

Only 60% of flights

The French DGAC civil aviation authority, which heads the ongoing investigation into the Germanwings crash, has asked airlines to cut their schedules for flights to and from France on Wednesday by 40%.

"Disruption is expected over the whole country," the DGAC said in a statement.

Air France says that it expects to operate almost all its long-haul flights but only 60% of its medium-haul flights to and from Paris Charles de Gaulle airport.

The DGAC, however, also asked airlines to cut 50% of their flights on Thursday.

Hundreds of cancellations in the UK

Low-cost airline Ryanair says it has had to cancel more than 250 flights to Birmingham, Luton, Leeds Bradford, Stansted, East Midlands and Dublin, with further cancellations likely.

In Europe, Ryanair's cancelled list includes flights to Alicante and Malaga in Spain and Marrakech in Morocco.

"We sincerely apologise to all customers affected by this unwarranted strike action and we call on the EU and French authorities to take measures to prevent any further disruption," the company said in a statement.

"It's grossly unfair that thousands of European travellers will once again have their travel plans disrupted by the selfish actions of a tiny number of French ATC workers."

Low-cost competitor easyJet has had to cancel 118 flights to and from France, including 10 to and from the UK.

"Like all airlines flying to and from France, we expect significant impact to our flights during this period," the airline stated. "Although this is outside of our control, easyJet would like to apologise to its customers for any inconvenience caused."

A statement by Stansted airport said: "Some flights to and from Europe may be subject to delay or cancellation".

Travellers have been advised to contact their airline, as well as check flight information on Flight Tracker pages on the airlines' websites.