Ryanair is battling to prevent employees from taking industrial action. Last year strikes over pay and conditions forced the Irish airline to cancel hundreds of flights.

Ryanair welcomed the Irish High Court ruling, saying all flights scheduled to depart on Aug. 22 and 23 from Irish airports would operate as normal.

But the airline said it regretted the decision by under 30% of its UK pilots to strike on Thursday and Friday in "support of unreasonable pay demands."

After the High Court decided against granting Ryanair an injunction to prevent the strike, the British pilots' union BALPA offered to call off the action if the airline agreed to a new framework of talks.

However, Ryanair turned down the offer and the British union said the strike will go ahead.

"Ryanair foolishly tried to stop our strike in the High Court today and failed. Despite that, we extended an olive branch to Ryanair as a way of getting back around the table and calling off strikes over the next two days," Strutton said in a statement.

Separately, a five-day strike by Ryanair's cabin crew in Portugal is underway but disruption to passengers appeared minimal, with no cancelled flights or major delays.

In a statement released on Wednesday afternoon, Ryanair said more staff than needed showed up to work at Portuguese airports on Wednesday morning and there would be no significant disruption to flights to and from the country during the rest of the day.

Portugal's SNPVAC cabin crew trade union met with the Portuguese Minister of Infrastructure and Housing on Wednesday to discuss the labour situation, including the impact of the possible closure of Ryanair's base in Faro.

SNPVAC president Luciana Passos said 70%-80% of crew members were currently on strike, though there were no major delays or cancellations at Lisbon, Porto and Faro airports.

"This (strike) is an attempt to once again draw attention to the problems faced by Ryanair crew members, to the way Ryanair operates in Portugal and the total impunity with which Ryanair operates," Passos said.

Ryanair's management says significant progress has been made since last year's strikes, with collective labour agreements concluded with a number of pilot unions throughout Europe.

But SNPVAC said Ryanair had refused to comply with a protocol signed last November, which it said included holiday pay, 22 days of annual leave per year and full compliance with Portuguese parental law.

At the height of the summer season, Portugal's government set out a minimum service for Ryanair and its staff to deliver, including a daily round trip between Lisbon and London.

SNPVAC said the minimum service order was "abusive" and undermined the right to strike.

Belgium's CNE and ACV PULS unions told members on Tuesday not to comply with a Ryanair request to staff flights affected by the Portuguese action.

Spain's STICPLA union also sent a letter to members, advising they were not obliged to "answer company calls" if they were in their rest time, on days off or on holiday.

Unions representing cabin crew in Spain said their plans for 10 days of strikes next month still stood after more than seven hours of mediated talks with the airline ended on Tuesday without agreement.