If the airline has overbooked the flight you are booked on, or for another reason which means the airline cannot put you on the flight, you may be ‘bumped’, which is also known as denied boarding. This means that the flight leaves, but you are not on it. You can sometimes be bumped with your agreement in which case you are a volunteer, or you can be bumped without your agreement in which case you are a non-volunteer.

In cases of overbooking, where you agree to give up your reservation, the airline and you must agree on what compensation you will accept. This might be vouchers. In addition, they must give you either a refund of the ticket price if you decide not to travel within seven days or an alternative flight with the same airline.

The refund could be the full ticket price if you decide not to travel, or the part of the ticket not used, and a return flight to the departure airport. This would depend on whether missing the flight you are ‘bumped’ from means you have missed what you were flying for, and your onward travel no longer has a point so you would like to return home.

If you do not want to have a refund, the airline must re-route you to your final destination as soon as possible, or at a later date if that suits you better.

If you choose to travel as soon as possible the airline must provide care and assistance while you are waiting for your new flight. If the re-routing goes to another airport in the destination city, the airline must pay for you to get to the original airport or a close-by destination of your choice.

If you choose to travel at a later date the airline is responsible for providing an alternative flight subject to availability, but it will not be required to provide care and assistance. 

If you are ‘bumped’ off your flight and giving up your reservation was not voluntary, then you are entitled to compensation known as denied boarding compensation. In order to qualify for compensation, you must:

• Have a valid ticket and travel documents
• Have a confirmed reservation
• Have checked-in by the deadline given to you by the airline

The airline must give you either a refund of the ticket price within seven days or an alternative flight, plus additional compensation based on the delay time of the alternative flight offered by the airline.

You are not entitled to reimbursements of any other components of your trip affected by the overbooking such as hotel or transfer costs at your destination unless you are on a package holiday. Being on a package holiday gives you extra rights

If you do not want to have a refund, the airline must re-route you to your final destination as soon as possible, or at a later date if that suits you better.

If you choose to travel as soon as possible the airline must provide care and assistance while you are waiting for your new flight. If the re-routing goes to another airport in the destination city, the airline must pay for you to get to the original airport or a close-by destination of your choice.

If you choose to travel at a later date the airline is responsible for providing an alternative flight with the same airline subject to availability.

The airline should provide you with meals and drinks, and hotel accommodation where appropriate while you wait for your flight. You may prefer to return home if it is possible to do so and return for your later flight, in which case you should inform your airline. 

On most other flights it depends on the airline. You may not get back as much as you expect due to how the airlines calculate the price of the seat they move you to. Most airlines will refund only on the sector affected.