Monarch customers only found out their flights were cancelled after the airline was put into administration on Monday (2 October).
The Civil Aviation Authority (CAA) said Britain's fifth-largest airline had ceased to operate with immediate effect, after failing to secure a temporary extension to its Air Travel Organiser's Licence (ATOL) for the third time in four years.
This meant it was no longer able to sell ATOL-protected holidays and has since appointed KPMG as administrators. Some 750,000 future bookings have been cancelled as a result, with around 110,000 Monarch customers stranded overseas.
Paul Wright was due to fly out to Mallorca from London Luton on 18 October to attend his brother's wedding but did not receive any notification from the airline.
"My family and I simply found out this morning when the news broke," he told IBTimes UK.
"We had no communication at all with Monarch, not even an email. It was obviously quite distressing as we are going over for my brother's wedding and it is such short notice. We have now had to book a separate flight."
Meanwhile, Britain's Transport Secretary, Chris Grayling, has described the demise of the Monarch airline as an "unprecedented situation", which would require an "unprecedented response".
The government has launched its biggest ever peacetime repatriation operation to fly the stranded passengers back to the UK at no cost to them, and Grayling said the government was working in partnership with the CAA to establish a temporary airline to carry out the operation.
The government has asked the CAA to charter more than 30 aircraft to bring back the tens of thousands of Monarch customers stranded abroad to the UK.
The aviation regulator added passengers due to fly back to the UK over the next two weeks do not need to cut short their stay and will be repatriated at no cost.
"This is a hugely distressing situation for British holidaymakers abroad - and my first priority is to help them get back to the UK," Grayling said in a statement issued by the Department for Transport.
"That is why I have immediately ordered the country's biggest ever peacetime repatriation to fly about 110,000 passengers who could otherwise have been left stranded abroad.
"Nobody should underestimate the size of the challenge, so I ask passengers to be patient and act on the advice given by the CAA."
Government "sat on its hands"
However, the government has been strongly criticised by the unions for "sitting on its hands" and allow Britain's fifth biggest airline to collapse. The carrier was hit hard by terrorist attacks in Turkey and Egypt, which saw its rivals turn toward Spanish destinations, traditionally one of Monarch's strongholds.
The Unite union insisted that the airline could have been kept afloat, had the government approved a "bridging loan", like German Chancellor Angela Merkel did when Air Berlin fell into insolvency in August.
The union said that continuing uncertainty surrounding Brexit and the ability of UK airlines to fly freely in Europe after 2019 undoubtedly hindered Monarch getting the investment it needed to restructure and survive.
"This uncertainty, combined with the apparent unwillingness of the government to assist at commercial rates and at a profit to the taxpayer, has left thousands of jobs at a great British airline hanging by a thread," said Unite national officer Oliver Richardson.
"Now is not the time for Government ministers to wash their hands of a problem they have contributed to. Ministers need to act fast by intervening in a similar way as their German counterparts did with Air Berlin and help secure a future for Monarch."
Speaking to BBC 5 Live, Grayling admitted the airline had been "a victim of a price war in the Mediterranean" and that he had "hoped up until the last few days that discussions with other airlines would help secure Monarch's future."
The Transport Secretary also hinted a number of other airlines could hire Monarch pilots, revealing he had "already spoken to other airlines who think they are a first rate team of people working for Monarch and are looking to try and hire some of them."
Wider malaise in the aviation industry
Meanwhile, Monarch's collapse will temporarily take the heat off Ryanair, which is undergoing a major crisis of its own after cancelling 2,100 flights between September and October and announcing 18,000 schedule changes between November and March 2018.
Shares in the Irish carrier were up 3% in early trading on Monday, while fellow budget airlines easyJet and WizzAir traded 4% and 2.6% higher respectively. However, while Monarch's demise will provide some relief to Ryanair, its collapse has wider implications.
"The third airline failure this year in Europe, after Alitalia and Air Berlin, is a symptom of over-capacity and overly-aggressive pricing," said Neil Wilson, senior analyst at ETX Capital.
"It means fewer seats to fill sector-wide – more than six million in the case of Monarch. This should mean Ryanair and easyJet can comfortably improve load factors, even if the reputation of the former has suffered of late. This should be positive for margins despite pricing pressures."