What Proof Is Required for a Multi Entry Tourist Visa Application to Thailand?

When applying for a Multi Entry Tourist Visa to Thailand, you need to provide proof that you will be leaving Thailand within 60 days of arrival. This does not necessarily have to be a return flight to the UK; as long as you have a ticket showing you will leave Thailand (to another destination like Cambodia, for example), it suffices. Some commenters noted that you don't need to present proof of onward flights every 60 days if your visa is valid for a longer period.