An artist's impression of the scene inside the High Court

Abdelbaset ali Mohmed al-Megrahi's sentence will be backdated to 1999 when he was first taken into custody.

The Libyan secret service agent was sentenced two years ago to life in prison for the 1988 bombing, with a recommendation that he served at least 20 years.

However, a change in the law meant Megrahi, 51, had to again come before the Scottish courts so that the punishment period could be set.

Pan Am Flight 103 exploded over the Scottish town of Lockerbie in December 1988, causing the deaths of 270 people.

In 2001, Megrahi was found guilty of their murder after an 84-day trial under Scottish law in the Netherlands. He was jailed for life.

I don't get my kid back so he should stay in prison. He murdered him deliberately Jack Flynn Relatives give their reaction

The judges, Lords Sutherland, McLean and Coulsfield, recommended that he serve a minimum of 20 years "in view of the horrendous nature of this crime".

However, the judges' sentence was merely a recommendation.

Human rights laws have since been introduced which mean that lifers must be told exactly how long they must serve before they can apply for parole.

After a four-minute hearing at the High Court in Glasgow on Monday, Lord Sutherland said of the bombing: "Quite clearly this was a wicked act carried out in the full knowledge that the plan, if successful, would result in the slaughter of many entirely innocent persons."

Relative's reaction

He indicated that Megrahi might have been sentenced to 30 years but they took into account his age and the fact that he was serving his sentence in a foreign country.

Megrahi will be 74 before he is eligible to apply for parole.

Amid heavy security, relatives of those killed in the atrocity sat just yards from Megrahi at the hearing.

After the outcome, Jack Flynn, an American whose son would have been 36 on Monday, gave an emotional reaction to the sentence.

He will have his day in court, we hope, and then all of us will know what really happened, perhaps, on the 21st December 1988 Eddie MacKechnie Megrahi's lawyer

"I don't get my kid back so he should stay in prison," he said. "He murdered him deliberately."

Mr Flynn pointed out that 27 years equated only to one month per victim.

"I would hope that he would spend the rest of his life in prison because of the number of people he deliberately killed," he went on.

"This was not a spur-of-the-moment decision where you kill somebody. He planned to murder these people over a number of years.

"I would want to see if we can change this because this was such a horrible crime."

Megrahi has been held in a special unit at Barlinnie Prison in Glasgow since March 2002, when his appeal against the conviction was rejected.

His lawyer Eddie MacKechnie said: "This was always going to be a difficult day for any convicted person.

The 1988 bombing killed 270 people

"As far as the future is concerned - this is what really matters - all this has done is accentuate the need for us to marshal all our forces to establish the innocence of this man.

"I have no doubt that we will have the opportunity for a fresh appeal in due course.

"He is looking forward in faith for a new day in court, probably the same court for all we know.

Asked what Al Megrahi's mood was, he responded: "His mood is one of faith and hope in his legal team and advisers, faith in justice and faith in his religion.

"I respect the gentleman. He will have his day in court, we hope, and then all of us will know what really happened, perhaps, on the 21st December 1988."