Cancun charter flights can be booked as seat only without restrictions except that a return flight must be booked and you are usually tied to fixed durations in multiples of one week so 7,14,21 and 28. There are no rules for the best way to get cheap Cancun flights but you will normally see cheapest prices for flights where there is some healthy competition so Gatwick for example can be cheap. This is not always true however, I remember when Thomson had Cancun flights from Cardiff and they were often keenly priced. Since the merger of the big four travel companies into “the big two” there are three places to look for flight only to Cancun – flythomascook.com , firstchoice.co.uk and thomsonfly.com
The flight time from UK airports to Cancun (CUN) is around 11 hours. The good news is that the new airport means getting through customs / passport control is fairly efficient and also that the transfers from the airport are fairly short whether you are going to stay in Cancun or Playa del Carmen. The longest transfers are to the hotels on The Riviera Maya such as The Akumal Beach Resort.
There are no scheduled flights to Cancun direct from the UK so apart from charter seat only, other options are normally via the USA, for example via New York or Miami but that turns the journey into a much longer and complicated affair so most people stick to the charter flights. Both Thomson Airways (which incorporates Thomsonfly and First Choice Airlines) and Thomas Cook Airlines (which incorporates MyTravel Airways and Thomas Cook) are increasing the seat pitch on their longhaul aircraft as well as improving facilities to include for example individual seat back TV screens. Thomson Airways will be the European launch customer of the Boeing 787 which will set new standards for in flight comfort with large windows and improved air quality and cabin lighting. That will be good news for Cancun flights.