Abdul Baset Ali al-Megrahi was driven in a police van from Greenock Prison to Inverclyde Royal Hospital. The convoy was escorted by armed officers and a police helicopter.

The former Libyan intelligence agent convicted of the Lockerbie bombing was taken from prison for hospital tests yesterday amid a huge security operation.

Abdul Baset Ali al-Megrahi was driven in a police van from Greenock Prison to Inverclyde Royal Hospital. The convoy was escorted by armed officers and a police helicopter.

It's understood that al-Megrahi, 56, underwent a scan during an outpatient appointment at the hospital in Greenock. Doctors are believed to have ordered the tests after concerns were raised about al-Megrahi's health.

It is the second time that al-Megrahi has required hospital treatment during his time in Scottish jails. He was transferred from Barlinnie prison to Glasgow Royal Infirmary in July 2003 after complaining of stomach pains. On that occasion he was returned to jail the same day after having tests for a suspected stomach ulcer.

Al-Megrahi is serving a life sentence with a minimum term of 27 years after being convicted in 2001 of bombing Pan Am Flight 103 in 1988. All 259 men, women and children on board died along with 11 residents in the town, who were killed when the wreckage crashed down, causing a huge fireball.

Al-Megrahi lost an appeal against his conviction in 2002 but was given another opportunity to clear his name in June last year when the Scottish Criminal Cases Review Commission referred his case back to appeal judges for a second time.

This week it emerged that the Appeal Court in Edinburgh had decided to appoint a special defender to view confidential documents believed to contain information about the electronic timer used to detonate the aircraft.

The court's decision came after an unprecendented hearing behind closed doors during which the UK Government argued that the documents should remain secret to avoid compromising security. David Miliband, the Foreign Secretary, claimed that handing over the documents would put national security at risk.

It will be the first time that a special defender has been used in a Scottish court, although the process has been used in English courts during terrorism cases. Lord Hamilton, the Lord President, sat with Lords Kingarth and Eassie last month to decide whether al-Megrahi can obtain a fair trial without access to the documents.

The Advocate General, Lord Davidson of Glen Clova, who represents the UK Government in the Scottish courts, asked the court to appoint a security-vetted lawyer to look at the documents on behalf of al-Megrahi's defence team before arguing which parts of the documents should be published.

The final decision on the release of sections of the document would lie with judges. The court has not yet formally published its decision but Kim Howells, the Foreign Office Minister, has written a letter confirming that the court has decided to appoint a special defender.

It is understood that al-Megrahi's legal team is planning to appeal against the decision to the Privy Council on the ground that the move would violate his human rights.

Dr Hans Koechler, the United Nations special envoy to the trial in the Netherlands of the two Libyans accused of the Lockerbie bombing, criticised the development as “intolerable”. Dr Koechler said that it was “detrimental to the rule of law”.

He added: “In no country can the situation be allowed where the accused or the appellant is not free to have his own defence team, and instead someone is imposed upon him.” It is expected that the full appeal by al-Megrahi will be heard next year.

Police, prison authorities and the health board all declined to give further details about al-Megrahi's condition last night. A Strathclyde Police spokeswoman said that they would not comment. A Scottish Prison Service spokeswoman said: “We do not comment on individual prisoners.” Health chiefs also refused to answer questions about the visit.

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