About 2,500 jobs have been lost and 64,000 bookings have been cancelled with the collapse into administration of Specialist Leisure Group.
Travel trade organisation Abta said the hotel and travel company had been "significantly impacted" by the coronavirus pandemic.
The company, which has its headquarters in Wigan, specialised in breaks and events for the over 50s.
It struggled to provide thousands of refunds for cancelled trips, Abta said.
It added that the vast majority of cancelled bookings were coach package holidays, which are financially protected. Customers with these bookings will receive a full refund, Abta said.
The Specialist Leisure Group included well-known coach holiday brands Shearings and National Holidays.
It also operated hotel businesses such as Bay Hotels, Coast and Country Hotels and Country Living Hotels.
The firm said on its website that all tours, cruises, holidays and hotel breaks had been cancelled and would not be rescheduled, and blamed the impact of the coronavirus pandemic.
John de Vial, Abta's director of membership and financial services, said: "Today is a very sad day for these customers and the thousands of staff who will have lost their jobs.
"The fact that two such well-known brands with a loyal customer base have had to call in administrators is a stark indication of the pressure that the holiday industry is under as a result of the coronavirus pandemic.
"Abta has repeatedly highlighted to the government the urgency of the situation and the need to set out a co-ordinated strategy with clearer communication if it wants to help avoid significant job losses and support companies to weather the storm."
Atol, the government-run financial protection scheme, said it would be contacting the small number of customers with flight-inclusive packages, which would be protected.
Atol spokesman Andrew McConnell said: "This is a particularly sad day for customers and employees of Shearings Holidays Ltd, a long-standing business and well-known UK travel company."