Many holidaymakers will be wondering how they can claim back money for their trips after the 178-year-old package holiday firm entered liquidation after last-ditch efforts to save it failed.
The company, which confirmed today it has ceased trading, had 21,000 employees worldwide and around 600 UK travel stores, as well as its own airlines.
How does Atol protection work and how do I know if I have it?
Atol is a scheme which aims to protect customers flying from the UK if a travel company they have booked a trip with collapses, ensuring they do not lose money or get left stranded.
The regulations mean those booking a flight or a flight-inclusive package should be issued with an Atol Certificate when they pay for their booking, if it is protected.
Those with Atol protection are entitled to a full refund for their cancelled holiday, according the government-backed Civil Aviation Authority (CAA).
Those currently abroad may also be able to claim for the cost of replacing Atol protected parts of their trip, and other costs they may incur due to their flights being cancelled or delayed.
"The Civil Aviation Authority will be launching a service to manage all refunds by Monday 30 September, once the flying operation has progressed," the CAA said.
"This refunds service will seek to process all refunds within 60 days of full information being received."
It has urged customers not to submit anything to the CAA in the meantime, while it deals with "the UK's largest ever peacetime repatriation" programme.
Atol protection applies to many air trips and holidays booked with UK based travel companies, including most package trips from Thomas Cook.
But not all holidays are Atol protected, including some that flights or hotel only, so check your booking to see if you were sent a certificate, which will also state who the trip is protected by.
If a certificate shows another airline which is not part of the Thomas Cook group, contact the travel provider listed.
If your flight or holiday is not Atol protected, you may still be able to claim from you insurance provider, credit card issuer or bank.
How do I make an Atol claim?
The CAA will launch a service to handle Atol claims for Thomas Cook customers on 30 September.
It said it will post further information on how to make a claim and how to find the form over the next few days on its website, but added that it is currently focusing on the "complex" repatriation programme.
In general, those with Atol protected holidays need to complete an Atol claim form and provide proof of the booking, of the Atol protection, and of payments they made to the travel provider.
Each claim is slightly different depending on the protection provided.
Details on how to complete the form can be found here, and include providing personal details, booking information and details about the failure of your provider.
For help and advice in settling disputes with Atol holders, you can also contact Citizens Advice, The Trade Association ABTA or The Travel Trust Association.
What if I am currently abroad?
Up to 150,000 people from the UK are currently on holiday with Thomas Cook.
The CAA and the Government have launched an operation to bring tourists home to the UK, with flights chartered for the operation from now until 6 October.
Details of flights scheduled by the CAA to get passengers back to the UK will be posted on the thomascook.caa.co.uk page, broken down by country.
Passengers are free to book alternative flights home themselves, but the CCA warns that it may not then be possible to claim back money for a flight under the Atol scheme if an alternate flight has already been arranged by the body.
The CAA adds that those with return flights booked as part of a package that are unrelated to Thomas Cook might still be running, so it's worth checking.
Passengers whose return flights to the UK are after 6 October may have to make their own travel arrangements to return home, but may also be able to claim back the cost if the original trip was Atol protected.
More information for affected passengers is provided by the CAA on a dedicated website here.Thomas Cook passengers who need further assistance can contact the CAA on 0300 303 2800 from the UK or on +44 1753 330 330 from overseas, but call charges apply.
Information will also be posted on the CAA's Twitter feed.
This article first appeared on our sister site the i.