Airlines have a right to refuse to carry passengers that they consider to be a potential risk to the safety of the aircraft, its crew or its passengers. 

Reasons will typically include if the passenger:

• is drunk or under the influence of drugs.
• has refused to allow a security check to be carried out on them or their baggage.
• has not obeyed the instructions of ground staff or a member of the crew of the aircraft relating to safety or security.
• has used threatening, abusive or insulting words towards ground staff, another passenger or a member of the crew of the aircraft.
• has behaved in a threatening, abusive, insulting or disorderly way towards a member of ground staff or a member of the crew of the aircraft.
• has deliberately interfered with the performance by a member of the crew of the aircraft of their duties.
• has put the safety of either the aircraft or any person in it in danger.
• or if the mental or physical state or health of the passenger is a danger or risk to themselves, the aircraft or any person in it.

Passengers must not do certain things while on board including:

• Endangering the safety of an aircraft
• Being drunk in an aircraft
• Smoking
• Disobeying a lawful command from the commander of an aircraft, and
• Acting in a disruptive manner (including interfering with the work of a member of the cabin crew).

If a member of crew deems behaviour disruptive, they have the right to take measures they think reasonable to prevent the passenger continuing that behaviour. When the aircraft lands, their actions may include:

• Making the passenger leave the aircraft; possibly under police escort
• Refusing to carry the passenger on the remaining sectors of the journey shown on their ticket, and
• Reporting the incident on board the aircraft to the relevant authorities with a view to them prosecuting for any criminal offences that may have been committed.

Serious offences could result in a large fine and/or imprisonment.