Alex Salmond yesterday raised the stakes in the cross-border dispute over the Lockerbie bomber, urging Jack Straw to allow the publication of all correspondence between the governments in Edinburgh and London.

The move by the First Minister followed the Lord Chancellor's letter in The Herald yesterday, in which he insisted the decision on whether Abdelbaset Ali Mohmed al Megrahi could be transferred back to Tripoli remains with Scottish ministers.

But sources revealed yesterday that a similar but confidential letter was sent by Mr Straw to the Scottish Government four days ago which had an extra paragraph, explicitly admitting that a prisoner subject to the controversial transfer agreement with Libya could take a case for judicial review - which would keep the decision in the hands of the Scottish courts.

A source close to Mr Salmond said: "Contrary to the letter in The Herald, Mr Straw wrote to the First Minister on February 11 and admitted for the first time that a decision made on this by Scottish ministers could be subject to judicial review. This is entirely different from his insistence that it is absolutely in the hands of Scottish ministers."

An excerpt from the letter, leaked to The Herald, states: "Naturally, as with any decision taken by a public body, a decision in relation to the transfer of a prisoner under the terms of the prisoner transfer agreement may be subject to judicial review."

The source added: "We have written to Jack Straw on the back of his letter in The Herald saying it would be in the public interest for all of the correspondence on this matter to be put in the public domain.

"Part of the international agreement for Camp Zeist was that anyone convicted of the bombing would serve their sentence in Scotland. To uphold the integrity of that process it would have been appropriate for them to have negotiated an exemption clause in the agreement."

Megrahi, who was convicted in 2001 of killing 270 people in the 1998 Lockerbie disaster, is appealing against his conviction and the case calls for a procedural hearing at the Court of Criminal Appeal in Edinburgh next week.

Talks began in secret some three years ago for the prisoner transfer agreement between Libya and the UK. Officials in the North African country have consistently said these talks centred on Megrahi, but Westminster has denied such claims.

Yesterday Mr Salmond said that in a meeting with Mr Straw last autumn, both sides appeared to be in agreement that anyone convicted of the atrocity would have to serve their full sentence in Scotland.

The First Minister added: "He took that point completely. He said he would negotiate that. He seems to have changed his mind or his mind has been changed. It is up to Jack to tell us why."

David Cairns, Scotland Office minister at Westminster, said: "Scottish Ministers will have the final say over any prisoner in Scotland's jails. Alex Salmond has known that since last summer and his anger is entirely synthetic.

"His comments about a potential judicial review are completely wrong. No ministerial decisions can be reviewed unless they are made incompetently.

"If Alex Salmond is serious about fearing a judicial review, what he is really saying is that he fears that his own minister, Kenny MacAskill, is unable to make a simple administrative decision safely."

Dr Jim Swire, whose daughter Flora died in the tragedy, said last night: "I would wholeheartedly agree with the move to make all the correspondence public. Because if there are doubts about the machinations of this deal it has been because of an absence of information and the fact the talks only became known about through a third party."