The British Airline Pilots' Association (Balpa) have confirmed tonight that negotiations with the airline operator have failed to reach an outcome to prevent strikes over pay and conditions.
BALPA general secretary Brian Strutton said: “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.
"We are extremely disappointed that Ryanair have taken such a belligerent and negative stance. We have become used to their macho posturing, but sadly it is their passengers who will pay the price for Ryanair’s attitude.”
The outcome could spell significant disruption for UK holidaymakers, with the possibility of delays or even cancellation of flights across Scotland and the UK.
There are several dozen Ryanair flights scheduled to and from Edinburgh today, as well as ten at Glasgow, around nine at Prestwick and a handful at Aberdeen.
Adam French, consumer rights expert at Which?, said after the decision: "The threat of more travel chaos over this busy bank holiday weekend will be a crushing blow for passengers who are likely to have spent weeks worrying about whether their holiday flights will take off.
"Ryanair now needs to take every possible step to minimise disruption by informing passengers likely to be affected and offering refunds or alternative transport as required by law in the event of cancellation - if necessary, on other airlines.
"The airline already has a track record of trying to shirk its responsibility to pay compensation to passengers when strikes by its staff go ahead, so we would expect the aviation regulator to step in and take strong action at the first sign of the airline trying to fob off its customers."
Edinburgh and Glasgow airports both told The Scotsman they did not expect flight cancellations tomorrow as a result of the strike, but advised all passengers to check for updates before travelling.
Pilots can be drafted in from elsewhere in Europe to fill in during strike action.
Ryanair had earlier today lost a High Court bid to block the ability of UK pilots to strike.
The airline said in a statement issued on its own website: "Thanks to the great work and volunteerism of the vast majority of our UK-based pilots, Ryanair now expects to operate its full schedule of flights to/from our UK airports on Thursday 22 and Friday 23 August.
"We do not expect significant disruptions on Thursday or Friday. However, we cannot rule out some small flight delays and/or flight changes.
"We are working hard with our pilot teams to minimise any such delays for our customers and their families.
"All passengers scheduled to travel on flights to/from UK airports on Thursday 22 and Friday 23 August should arrive at their departure airport as normal and they can expect their scheduled Ryanair flight to depart on time."
Mr Strutton said: "Ryanair was foolish to bring this into the High Court rather than the negotiating room.
"We offered to meet Ryanair management at Acas to negotiate a resolution, but instead they attempted a legal bludgeon. That's backfired.
"However, we are clear that we want to settle the dispute and bring about a change in Ryanair for the better.
"Pilots in Ryanair are seeking the same kind of policies and agreements that exist in other airlines – our demands are not unreasonable."
A second round of strike dates have also been set for next month.
Paul Gott QC, for Ryanair, told Mrs Justice Lambert during the hearing that strike action could be "enormously disruptive", and Ryanair would suffer "significant reputational" damage.
Mr Gott submitted that Balpa had not conducted a ballot that complied with the requirements of labour relations legislation.
But Mr Strutton said: "We want to address issues like pensions; loss of licence insurance; maternity benefits; allowances; and harmonise pay across the UK in a fair, transparent, and consistent structure.
“We hope that Ryanair will take up our offer of a way forward this evening so we can call off this action. We urge Ryanair to change their attitude to dealing with us, and adopt a constructive approach.
“In the event that Ryanair rejects our overture and therefore the action over the next two days does go ahead, we apologise to the passengers who will be affected. Such action could have been avoided if Ryanair adopts a different approach.”