Britain's main air traffic control provider has rejected complaints by Ryanair that staff shortages in UK air traffic control contributed to flight delays at Europe's largest low-cost airline on Sunday and Tuesday.

Ryanair has said air traffic control (ATC) strikes in France and ATC staff shortages in Spain, Germany and Britain have caused a surge in flight delays and cancellations this year.

The Irish airline has taken to providing daily updates on Twitter of how many flight delays are down to ATC, reporting that "French, German, Spanish and UK ATC staff shortages caused delays to over 1,000 ... flights" on Sunday.

On Tuesday morning, it said ATC staff shortages in France, Germany and Britain had caused 82 delays.

But Britain's national air traffic control provider NATS, which says it handles 25 percent of European traffic, has rejected the criticism in its own posts on Twitter.

"There were actually no ATC staffing delays in the whole of the UK yesterday," it said on Monday, with a similar tweet on Tuesday morning.

In response, Ryanair said British and German ATC providers were not "rostering enough ATC staff to cater for the number of flights that are scheduled to operate."

A NATS spokesman dismissed that.

"The categories of delay are set across Europe and all ATC providers are required to report against them using a strict set of criteria laid down in international law. We don't just make it up," he said.

He said NATS had written to Ryanair to offer a face to face meeting to explain how record levels of traffic this summer mean it has to sometimes restrict capacity to maintain safety.

Data published for June 2018 by network manager Eurocontrol showed NATS' staffing delay in Britain represented less than 0.5 percent of total air traffic flow management delay in Europe, NATS added.

Eurocontrol said last month it expected 14.3 million minutes of delay for 2018, 53 percent more than in 2017 because of strikes, capacity/staffing shortages and weather.

Ryanair canceled thousands of flights last year after punctuality rates collapsed due to a shortage of standby pilots. The airline says it has since resolved the issue, but is facing several strikes from staff demanding better conditions.

A Ryanair spokesman said it had not experienced any flight delays or cancellation due to a shortage of flight staff in recent weeks.