Scotland's most senior judge today launched an unprecdented attack the country's chief prosecutor over her reaction to the collapse of the World's End murder trial.

The Lord Justice General criticised Lord Advocate Elish Angiolini over a speech made to the Scottish Parliament in the wake of the case's dismissal from the courts last month.

The law officer insisted to MSPs that there had been enough evidence to prosecute Angus Sinclair for the murders of teenagers Christine Eadie and Helen Scott.

But today Lord Hamilton, Scotland's most senior judge, took the unusual step of writing a strongly-worded letter to Ms Angiolini describing her comments, which implied judge Lord Clarke was wrong to dismiss the case, as "inappropriate".

In the letter, which was made public, he wrote: "Public criticism in a political forum of particular decisions, especially in controversial and sensitive areas, is in my view inappropriate."

The case against Sinclair, a convicted killer and paedophile, was thrown out at Edinburgh High Court last month after Lord Clarke ruled that there was insufficient evidence for the jury to reach a verdict.

The trial collapse caused further heartache for the family of the two teenage victims killed 20 years ago.

It also raised questions of the Crown's presentation of the case.

There were calls for a public inquiry by politicians who said that advocate-depute Alan Mackay had not led all the available evidence during the trial.

And criticisms were made over the Crown's decision to bring forward a prosecution at all if a conviction was not likely.

The Lord Advocate's statement to Parliament on September 13 was prompted by the attacks.

She defended her department's handling of the case in the speech, describing its collapse as "deeply disappointing".

The Lord Advocate insisted: "I am of the clear opinion that the evidence made available to the court was sufficient to be put before the jury to allow them the opportunity to decide on the case against Angus Sinclair."

But in his letter today the Lord Justice General wrote: "It is clear that you were, as Lord Advocate, stating to the Parliament that in your "clear" opinion there was sufficient evidence to go to jury.

"The plain implication from that statement was that you were publicly asserting that the decision of the trial judge was wrong."

He went on: "I am concerned that you have thought it appropriate to challenge, in a public and political forum and in the way which you have, a final decision of the court (whether that decision be right or wrong)."

The Lord Advocate concluded: "I can readily understand that, given the issue which had arisen as to whether the Advocate depute had properly exercised his discretion as to what evidence he should lead (or not lead), you would find it appropriate publicly to support him.

"But such support could have been afforded without public criticism of the judge."

In a letter of response to Lord Hamilton, the Lord Advocate said she had chosen her words to Parliament "with great care".

Ms Angiolini stated that her comments related to her department's decision-making "and not anyone else's".

She wrote today: "I considered that it was important for me to allay public concerns as quickly as possible and that this should be done by a full statement to the Parliament.

"I chose my words to the Parliament with great care.

"I explained the background to and the basis of the Crown's decision-making in the case and sought to address the concerns which I have set out above.

"In doing this I stressed the independence of the judiciary and the need to respect that.

"I repeated this during questions following the statement.

"Indeed, in almost six years as a law officer I have avoided any public criticism of judicial decisions.

"My comments were about the Crown's decision-making, and not anyone else's."

The Lord Advocate stated: "I do not think I could have gone further expressly to afford greater respect for the final decision of the trial judge in the circumstances."

The First Minister, Alex Salmond, said during First Minister's Questions that Ms Angiolini was "absolutely right" to make a statement in Parliament about the collapse of the case.

"Given the public interest and concern in this case, no member of this Parliament and I think very few people in Scotland, would expect anything less," he said.

"Inevitably in giving that statement and then answering questions, the Lord Advocate is going to put forward the crown point of view - the prosecution service's point of view, as indeed was done in open court.

"I don't believe that should be taken as a direct criticism of a trial judge.

"That is surely a law officer responding to public concern, subjecting herself to parliamentary scrutiny."

Mr Salmond added that judicial independence is guaranteed in Scotland and a forthcoming Bill will further underline this.