A summary of this complicated area:
Each country operates its own rules to ensure consumer protection, and the UK (where we are based) has some of the most stringent requirements around, mainly inherited from the European Union (EU). In summary, any UK company or individual offering travel arrangements available for sale in the UK and that involve any flight as part of the arrangements (a 'flight-inclusive holiday') has to hold an Air Travel Organisers Licence (ATOL), granted by the Civil Aviation Authority (CAA).
In addition, any company that sells a 'package' (any combination of more than one of the following: flights, hotels, car hire, other ground arrangements such as transfers) must be bonded through an approved body.
There a few areas that can fall outside the scope of the above (for example if you buy just accommodation abroad, and have bought your flights elsewhere).
Scheduled airlines do not have to hold an ATOL (charter ones do) so there is another potential grey area here, although most ATOL holders are obliged to offer refunds or alternative flights should an airline fail.
So you should always check that the company you are booking through has either an ATOL (if there are flights involved), or some other recognised protection arrangement. If not, or if you make booking directly for hotels or services, then you will not be covered if the company through who you book goes out of business after you have paid them.
Several organisations, including the Association of Independant Tour Operators (AITO), the Association of British Travel Agents (ABTA) operate or recommend protection schemes which cover travel not already covered by the ATOL system (i.e. anything without a flight).
In our case we hold an Air Travel Organisers Licence (ATOL) number 2793, from the Civil Aviation Authority, as required under EU Regulations, which guarantees the security of holidays sold in the UK that include flights. For all other bookings from clients within the UK we insure our passengers with the ABTA-approved insurance firm IPP (International Passenger Protection Limited).
If you do not receive an ATOL Certificate then the booking will not be ATOL protected. If you do receive an ATOL Certificate but all the parts of your trip are not listed on it, those parts will not be ATOL protected. For more information about financial protection and the ATOL Certificate go to www.atol.org.uk/ATOLCertificate.