Procedures for loading baggage at Heathrow airport came under scrutiny yesterday at the trial of the two Libyans accused of the Lockerbie bombing.

Staff working at the airport on the night of the 1988 disaster told the court at Camp Zeist in Holland how bags were transferred on to the doomed flight.

The hearing heard that construction work was going on at the time and security guards were not on duty near the baggage area, a practice which changed after the disaster.

One traveller due to board PanAm Flight 103, which exploded over Lockerbie killing all 259 passengers and crew, missed the flight completely because he was drinking in the bar at Heathrow.

The prosecution alleges that the two accused, Abdelbaset Ali Mohmed Al Megrahi, 48, and Al Amin Khalifa Fhimah, 44, were involved in placing an unaccompanied suitcase containing a bomb on board an Air Malta Flight to Frankfurt from Luqa Airport, Malta, where they worked for Libyan Arab Airlines. At Frankfurt it was allegedly tagged to join PanAm Flight 103 to New York via Heathrow, with the suitcase allegedly transferred from the Frankfurt plane to the New York plane when it arrived at Heathrow.

The court heard how passengers arrived at Heathrow from Frankfurt on flight 103A on the night of December 21 before being transferred to PanAm Flight 103, which exploded over Lockerbie, killing 11 people on the ground.

Mr Peter Walker, who worked as a baggage supervisor for PanAm at Heathrow, described how their luggage was transferred on the tarmac directly from one plane to the other.

About six bags from the interline shed at Heathrow, which held luggage from other connecting flights, were brought on to the tarmac in a container, and the luggage from the Frankfurt flight was placed into the same container and loaded on to the New York flight.

The rest of the luggage loaded on to the plane came from passengers who started their journeys at Heathrow and whose bags went directly from check-in to a place known as the baggage build-up area, and from there to the aircraft.

As Mr Walker was cross-examined by defence counsel Jack Davidson, it emerged that the container from the interline shed was brought into the baggage build-up area before bags were picked up from the Frankfurt plane. And the court heard security guards were not on duty in the immediate area.

Mr Davidson asked Mr Walker: ''If a person had been going about that baggage build-up area wearing a uniform and a security pass, would that person appear to you to be a genuine employee?''

Mr Walker replied: ''Yes.''

The court also heard from lead agent Nicola Milne who worked for PanAm, dealing with passengers at Heathrow. She said staff became aware that a passenger named Mr Basuta had checked in for Flight 103 but was not on the plane in his seat when it was ready to depart. He was eventually found after the flight left and said he had ''been at the bar'', Mrs Milne said. Mr Basuta had checked in two bags which travelled on the plane without him.

Fhimah and Megrahi, alleged members of the Libyan Intelligence Services, deny conspiracy to murder, murder and a breach of the 1982 Aviation Security Act.

Mr Alan Berwick, who in December 1988 was manager of corporate security for PanAm at Heathrow, described how interline bags from a connecting flight were dealt with.

''At one stage the interline bags, if not positively identified at the time of check-in, were sent to the side of the aircraft until the person showed up. If the person showed they were loaded, if not they weren't,'' he said.

However the court heard that this passenger/baggage reconciliation procedure, which would ensure a passenger and their baggage travelled on the same aircraft, was changed before the disaster, and interline baggage was instead X-rayed. The reconciliation system was reintroduced in the aftermath of the Lockerbie bombing. Prosecuting counsel Alan Turnbull QC asked him: ''Once the positive reconciliation had been dispensed with, would it have been possible for someone to abuse the PanAm interline system by sending an unaccompanied bag?''

He said: ''In my opinion it would be possible.''

Mr Berwick said Heathrow staff were made aware of the ''Toshiba'' and ''Helsinki'' warnings prior to the disaster. The first warned them to look out for explosive devices built inside Toshiba radios which could be put on board aircraft, following the discovery of such a device in Germany. The Helsinki warning alerted staff to the possibility of a lone Finnish woman being duped into carrying an explosive device on to an aircraft.

The trial continues today.