Under UK261, denied boarding means refusing to carry passengers who have presented themselves for boarding on time with a confirmed reservation. Refusals on reasonable grounds, such as health, safety, security or inadequate travel documents, do not count. The CAA says airlines sometimes sell more seats than the aircraft has, because some passengers do not turn up. They may also use a smaller aircraft than planned.

How it works

• Passengers must check in by the time the airline, tour operator or an authorised travel agent gave in writing or, if no time was given, at least 45 minutes before the published departure time.

• The airline must first ask for volunteers to give up their seats in return for benefits agreed with them. Volunteers also get a refund or an alternative flight.

• If there are not enough volunteers, the airline can refuse boarding against passengers’ will. It must then pay compensation immediately: £220, £350 or £520 depending on flight distance. It can halve this if the alternative flight arrives within two, three or four hours of the original arrival time.

• Bumped passengers also get care, such as meals and a hotel if needed. They can choose a refund within seven days or re-routing.

Why it matters for travel businesses

• Compensation is paid in money unless the passenger signs to accept vouchers or other services.

• Airlines must give priority to people with reduced mobility, those travelling with them and unaccompanied children.

• A passenger with reduced mobility refused boarding for safety reasons, or because the aircraft or its doors are too small, has the same right to a refund or re-routing.

• The CAA says refusing a passenger without a valid passport is reasonable. That is not denied boarding, so no UK261 compensation is due.

Our flight delay and cancellation guide has more.