Labour called for the inquiry after its Holyrood leader, Iain Gray, told MSPs that Mr Salmond claimed in September 2007 that cutting class sizes to 18 for pupils in primary 1-3 would be delivered in the lifetime of this Parliament.

Two months previously, however, a senior civil servant told education experts that “the scale of the commitment does not allow it to be delivered in the lifetime of a Parliament”.

At First Minister’s Questions yesterday, Mr Gray produced a minute of the meeting between the deans of the faculties of education and civil servant Donald Henderson revealing the advice to ministers that the pledge could not be met.

Mr Gray said: “The First Minister told this chamber the exact opposite two months later. I remember the look on Fiona Hyslop’s face when he said it. She knew it was not true.

“The First Minister misled this chamber on September 5, 2007. He made a promise he knew he could not keep. And then he left his Education Secretary to dangle. How must Fiona Hyslop have felt sitting there, tied to a promise they both knew was impossible?

“And in the end, he sacrificed her to save his neck. Fiona Hyslop was just the scapegoat. He is the guilty man. It is the mark of the man, the mark of this First Minister, to cast aside one of his own colleagues to save his own skin.”

The minute was uncovered by Labour MSP Hugh Henry under Freedom of Information and he is demanding an investigation.

He said: “The evidence would suggest that Alex Salmond has misled Parliament.

“It is unbelievable that the First Minister would not have been told. It’s now up to Alex Salmond to prove he did not mislead Parliament.

Tory deputy leader Murdo Fraser said it was “inconceivable” that Mr Salmond was unaware that his own advisers had made it clear the class size pledge could not be met.

He said: “This leads to the uncomfortable conclusion that either Alex Salmond knowingly misled Parliament or his own colleagues hid the truth. The SNP Government must immediately publish all advice given to ministers on this issue to clarify who knew what and when.”

A spokesman for Mr Salmond said the information had been in the public domain since February 2008 and had been raised several times by Labour.

He said Ms Hyslop had not informed Mr Salmond of the civil servant’s view because she, along with Finance Secretary John Swinney, was working on the concordat with local authorities to deliver reduced class sizes.

The new row blew up just 48 hours after Ms Hyslop lost her job as Education Secretary, and Mr Gray said: “Alex Salmond has already sacked Fiona Hyslop this week and now he has stuck the knife into her.

“It is just not credible that official advice on a central government policy would not be copied into the First Minister.”

MSPs had earlier endorsed the appointment of Mike

Russell as Ms Hyslop’s successor. In the debate that followed, Mr Russell called on critics to stop making a “crisis out of a problem”.

He was forced to defend the Government’s record on education after wide criticism of his predecessor for falling teacher numbers and slow progress on reducing class sizes.

Mr Russell admitted things were not “hunky dory” and urged other parties to back the intended reforms.

He said: “The ambition is to have that world-beating education service that draws together pre-school, schools, colleges and universities with a commitment to keep moving to achieve the highest standards and always to achieve the highest standards for those who are within it.”