The captain and co-pilot of a plane landing at Heathrow Airport were forced to wear oxygen masks after a strong smell made them feel dizzy and nauseous, a report has revealed.

The report by the Air Accidents Investigation Branch (AAIB) said that despite the co-pilot suffering eye irritation, the pair landed the Lufthansa Airbus A321 from Frankfurt safely.

When the co-pilot complained of being dizzy, the crew put on their oxygen masks and requested priority-landing clearance.

After the pilot established there was a similar odour in the passenger cabin, they informed the crew, 139 passengers, ground control and the fire service.

On landing, the engines were shut down and the situation in the cabin improved, with a few passengers still reported slight throat irritation.

The crew of six were taken to hospital for examination and blood tests, although nothing was found.

The report described the situation, which affected the aircraft on October 21, as serious.

Examinations on the aircraft were carried out at Heathrow and in Frankfurt on the plane’s return but the source of the smell could still not be determined.

The AAIB report said: “The investigation was inconclusive in that a source of the apparent contamination of the cabin and flight deck air was not found, despite the detailed analysis of residues and the medical examinations of the affected members of the crew.

“This event thus joins a growing number of cases in which there has been a similar lack of conclusive evidence as to the cause(s) of aircraft cabin air quality issues.”