Kiss Flights has become the latest British travel company to collapse, sparking uncertainty for an estimated 70,000 holidaymakers.
The budget firm sold flights to Greece, Egypt, Turkey and the Canary Islands.
The Civil Aviation Authority said travellers abroad who had flown with Kiss would get home as normal.
And anyone due to travel from the UK before 1800 BST on Wednesday is guaranteed their flight out and return after their holiday, the CAA added.
Kiss currently has about 13,000 customers overseas and 60,000 people have forward bookings with the company.
The "vast majority" of people who had booked future trips with the firm would receive refunds, the CAA said.
London-based Flight Options, which has owned Kiss since January last year, ceased trading at 1700 BST on Tuesday.
Travel journalist Simon Calder told the BBC that "bookings were not coming in for September and October that were needed for cashflow".
Last month Goldtrail, which specialised in holidays to Greece and Turkey, collapsed, affecting as many as 50,000 travellers.
And last week Birmingham-based travel firm Sun4U folded, leaving about 1,500 people stuck abroad, mostly in Spain.
In all, 13 travel firms have gone bust in the UK this year as a result of the recession, belt-tightening by travellers and the Icelandic volcanic ash cloud that threw European travel into turmoil. That compares with 33 last year.
Flight Options has bought a string of travel firms since it was launched in 1995 as a small tour operator offering seats only on various routes across the Mediterranean.
A statement on its website read: "As of 1700hrs on 17 August the Flight Options group of companies have ceased trading.
"The Civil Aviation Authority have been informed and we are awaiting further advice on the situation."
A spokesman for the CAA said: "We are picking up the pieces. People abroad will be fine.
"We will make sure everyone will be able to come back from their holidays. We will also make arrangements so that all of the people who were Atol [Air Travel Organisers' Licensing] protected will received full refunds. That will be the vast majority."
Clive Rees, from Llandrindod Wells, Powys, was due to fly to Turkey on Monday with Kiss, and had previously booked with Goldtrail when it collapsed.
He told the BBC: "We're very frustrated, it's a real nuisance... We've already had to rebook flights because of Goldtrail's collapse, and we're now looking around for cheaper flights."
Gary Johnson, from Colwyn Bay, was due to fly to Sharm El Sheik with Kiss flights in just over a week. He said his family's plans were ruined.
"We're just absolutely gutted, really are, because we can't get hold of anybody to let us know what is going on or ask them any advice... It's just disgusting really." His trip was a family holiday before his daughter goes to university.
Travel analyst Bob Atkinson, of www.travelsupermarket.com, said: "Unfortunately for some, it may be the case that some unlucky holidaymakers will be affected all over again.
"At this stage it is unclear how many passengers will be protected by the Atol scheme and we are waiting for advice from the CAA.
"This is sadly yet another collapse in what could become a rash of company failures this autumn."
Mr Calder said it was "not surprising" that a number of the "smaller players" were going bust in the current economic climate, but the timing of the recent collapsing was "surprising".
"Here we are, two weeks before the end of August and it is the third significant failure during the school summer holidays," he said.
"Normally travel companies which are going to go bust do the decent thing and wait until the middle of September when the earnings are no longer coming in but the bills most definitely are.
"It's really disconcerting for people, and not just the tens of thousands who have booked to travel with Kiss flights in the next few weeks but also people travelling on other companies who are wondering what's going to happen."
However, he said he did not think there would be any further significant collapses of travel companies this summer.
Some analysts believe the new coalition government's spending cuts are affecting consumer confidence, which is impacting the travel industry.
"There was a real drying up of business in the early part of the summer when the volcanic ash crisis hit, but then it bounced back pretty well," Douglas McNeil, transport analyst at Charles Stanley, told Radio 5 live's Wake Up To Money programme.
"But since the Budget in June the penny has dropped that austerity measures are on the way, which means the latter part of the summer has been pretty weak".