The Scottish Secretary, Alistair Darling, has come under attack after his first appearance at the despatch box in the Commons in his new post.
Mr Darling faces the opposition in the Commons
Mr Darling, who is also the UK transport secretary, described the Scottish Parliament as "the assembly" during the monthly Scottish Questions session.
A Scotland Office spokesman said later that it had been a "slip of the tongue".
His departure from the chamber before the Advocate General Lynda Clarke had finished answering questions led to the Scottish National Party claiming Mr Darling's time for Scottish affairs would be negligible.
Mr Darling has been hailed by Labour as Scotland's "direct voice" at Westminster following Tony Blair's cabinet reshuffle.
The MP for Edinburgh Central answered a series of Scotland-related questions from fellow MPs on a range of issues in the last Scottish Questions before the summer recess.
Mr Darling has already appeared before the Scottish Affairs Committee to outline what he saw as his role combining the two jobs.
BBC Scotland Westminster correspondent David Porter said the opposition parties concentrated on what they see as a conflict of interests between the roles.
Alex Salmond, Scottish National Party (SNP) leader at Westminster, said the move had led to "mass
confusion" and that his time for Scottish affairs would be negligible.
It was a blunder of the first order, getting him off to the worst possible start
SNP Westminster leader
In a statement, Mr Salmond said: "What we had from Alistair Darling and the semi-detached ministers in the Constitutional Affairs Department was mass confusion.
"The mistakes simply confirmed that the arrangements for dealing with Scottish business at Westminster are shambolic.
"First, Alistair Darling is so out of touch with Scotland that he talked about a Scottish 'assembly' rather than the parliament - and didn't even bother to correct himself.
"It was a blunder of the first order, getting him off to the worst possible start."
Mr Darling will have to decide in a few months time on the question of airport expansion in the UK, meaning he may have to choose between Scotland and England.
In the meantime, he told Scottish Questions that the review was not finished and he did not have to make the decision yet.