A senior flight attendant noticed spots on the arm of Patricia Roa, a 59-year-old Spanish woman, and asked her to leave the plane before take-off at Madrid's Barajas airport last Wednesday.

Mrs Roa, who has suffered for ten years from prurigo nodularis - an itchy skin condition that is non-contagious - tried in vain to explain the nature of the disease.

A doctor who happened to be on board confirmed the diagnosis and Mrs Roa telephoned her dermatologist who offered to fax the airline a medical certificate giving permission to fly.

But staff refused to listen and order the woman and her daughter off the flight which was bound for Trapani, in Sicily. Five officers from Spain's civil guard boarded the aircraft to escort them off after the pair refused to go quietly.

"I was told several times that they did not care what the disease was and that as I could not prove it was not contagious I couldn't fly," Mrs Roa wrote in a complaint lodged with police against the airline.

She said she had travelled all over the world and never experienced a similar problem. This was the first time she had attempted to fly with the budget airline.

A spokesman for the Dublin-based airline told Spanish newspaper El Pais that there was a clear company policy on such matters.

"Passengers suffering from a disease that could be considered or appears to be contagious must carry a medical certificate stating that they are fit to fly and pose no risk to other passengers and crew."