Holiday firm All Leisure Holidays has stopped trading, with hundreds of customers overseas.
It operated the Swan Hellenic and Voyages of Discovery cruise lines, which both cancelled New Year cruises at short notice.
The Civil Aviation Authority (CAA) said it will ensure the company's 400 holidaymakers currently abroad will be repatriated at no extra cost under the terms of the Atol protection scheme.
The "vast majority" will be able to return to the UK using the scheduled airline tickets included as part of their booking, the CAA added.
Travel trade organisation Abta said around 13,000 All Leisure Holidays customers were due to travel on future departures.
These have now been cancelled and a full refund will be given.
Around two-thirds of customers are protected under the Atol scheme, which covers flight and cruise packages, with the remaining holidaymakers on UK departing cruises able to get their money back through Abta.
Andy Cohen, head of Atol at the CAA, said: "We understand this will be concerning news for anyone who has booked to travel with the company.
"However, the Atol scheme exists for exactly this kind of situation and we are making immediate arrangements so all Atol protected customers can claim full refunds as quickly as possible.
"We are also arranging for people currently overseas to get back home to the UK at no extra cost - meaning no-one will be left stranded abroad."
The CAA set up a dedicated helpline for those affected on 0808 164 8810.
Further information is available at www.atol.org.uk and a refund claim form will be available shortly, the CAA said.