The future of a pioneering operation hung in the air when staff refused to transport the cells from Bristol International Airport.

A Bristol University professor has spoken of his fury at being forced to shell out £14,000 to hire a private jet to ensure the cells, to be used in the world's first windpipe transplant operation, reached a Barcelona hospital in time.

The jet was used after budget airline easyJet refused to let a courier take them on its scheduled service at the last minute.

Prof Martin Birchall said easyJet's refusal followed months of attempts to ensure the vital package was cleared for travel. It left him with just 14 hours to get the cells to Spain.

The airline insists it has no record of any request for security clearance to transport the cells, which are carried in a liquid to protect them.

Earlier this week, the Western Daily Press reported that Bristol University scientists used pioneering research to take the cells from Colombian Claudia Castillo's bone marrow and transfer them into a donated trachea. It meant surgeons in Spain could replace the patient's windpipe with the donated organ.

The technique saved the life of the 30-year-old, who is the first person in the world to be given a whole laboratory-engineered organ.

But the experiment was put at risk when the staff refused to allow the box containing the cells onboard.

Staff deemed German medical student Philip Jungerbluth, who was tasked with transporting the cells, a security risk because the contents of the box they were in exceeded the 100ml limit allowed on flights.

Prof Martin Birchall, who had grown the cells in his laboratory, said he had been in contact with the airline for a couple of months before the flight, and believed any problems had been dealt with.

He said he was told the package – containing about 60 million cells – could be taken on the plane as long as it was wrapped and labelled.

He said: "I phoned and couldn't get through to anybody, I emailed and didn't get replies and in desperation, I went to the desk at Bristol Airport and they put me through to people at their head office who told me what I needed to do.

"They gave me strict instructions as to how I should present something like a transplant organ, clearly labelled. They knew there was liquid and that it was packaged in a way that it would not get out."

Prof Birchall said that he had even phoned easyJet again an hour before setting off to the airport to check everything was in place.

He said: "On arrival, they said it couldn't go on because it would be a security risk but I had been talking to people on a regular basis. I almost got arrested by armed police; I was so furious, trying to explain months of work."

Prof Birchall said: "I was sat down feeling glum when Philip said he had a friend from medical school who used to fly and within a couple of phone calls he got him to leave Germany and be with us and he said he would charge us cost only."

Prof Birchall was reimbursed by the university and easyJet offered to refund the cost of the original flight.

An easyJet spokesman said that the airline worked with transplant organisations and organs can usually be transported by their planes throughout the UK with prior arrangement.

He said because the stem cells were placed in liquid, they would have been subject to stringent aviation rules with security clearance required.

A letter would usually be sent to the individual to show at check-in and security staff would have been alerted.