A disturbing video shows the moment an airline passenger was slapped and restrained by a UK immigration officer.

The man, understood to be an Afghani asylum seeker, was on board the Turkish Airlines flight from London Heathrow to Istanbul when video taken before take-off captured the incident.

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He could be seen screaming and crying for help as one immigration officer forced his head against the cabin and slapped him across the face, according to nearby passengers.

The footage was captured by Ahtzaz Ali, 27, an office manager from Birmingham, who was travelling to Syria to help refugees.

"There was a man who was clearly upset on board the plane but wasn't being abusive to the crew or anybody else," Ali told the Press Association.

"All of a sudden, someone who seemed like they were an immigration officer came and started physically abusing the man by slapping him and pushing his face down whilst he was crying and shouting that he wouldn't be safe going back to Afghanistan.

"The journey after he was taken off the plane was very upsetting as passengers were in tears, clearly disturbed by what they had seen.

"It was a violation of this man's human rights and shocking to see how he was being treated."

A Home Office spokesman said it did not comment on individual cases, but added: "If people are in the country illegally and refuse to leave voluntarily we will take action to remove them.

"Whilst it is regrettable that some people become disruptive on removal, we do our utmost to try and minimise any potential impact on the rest of the passengers.

"Any use of force must be fully justified and proportionate and is used only as a last resort for the shortest time possible."