The Manufacturing Science and Finance Union (MSF) said there has been an increase in attacks on staff - arising mainly from delays and disruption to flights.

John Andrew: The MSF says there has been an increase in attacks

It said staff feared that the delays in issuing passports over the past few months will make holiday-makers less tolerant of any delays this summer.

The MSF has agreed a policy with Lufthansa Ground Services on training staff to deal with confrontation and counsel anyone who is attacked.

Roger Lyons: Staff should not be at risk

General-Secretary of the MSF, Roger Lyons, said: "The agreement with Lufthansa is very welcome. It is also very necessary because in the service industries it is taken for granted that some people are peaceful and law abiding but some are not and take it out on staff.

"They have an important job to do and they should not be at risk.

"Too many people take out their frustration on staff. It is quite cruel and it has got to be stopped."

Staff fear an escalation of incidents in the summer

One check-in worker, who did not want to be named, said there was a "ground rage" incident at Heathrow airport virtually every week.

"It's usually verbal abuse, shouting and swearing but I have heard of physical attacks happening.

"Passengers obviously get annoyed when there is a delay, but most are patient and understanding. It's just a small percentage who lose their tempers and take it out on us.

"Our jobs are stressful, especially at busy times, and we can do without being verbally abused by people we are trying to help."

High-profile incidents

Earlier this year UK airlines began to log all new cases of so-called air rage amid growing concern that passenger anger and violence is increasing.

The Civil Aviation Authority (CAA) has asked all UK passenger airlines to supply it with details of all cases, following a number of high-profile incidents.