NICOLA Sturgeon has been urged to learn from Labour's mistakes and bring back a ban on parliamentary assistants sitting on the Holyrood committees that are supposed to hold their bosses to account.

The First Minister has moved to make a string of junior MSPs aides to cabinet members with a policy brief directly linked to the committees they sit on, in what critics say presents a clear conflict of interests and will weaken the vital role of the groups in scrutinising Government.

Kezia Dugdale, the Scottish Labour leader, admitted that her party had on occasion proposed the appointment of ministerial aides to relevant committees when it was in power, but admitted: "We were wrong then, as you are wrong now."

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She told Ms Sturgeon she risked making "the same mistakes in power that we once did" if she did not take steps to improve the independence of committees and parliamentary scrutiny of Government by reintroducing a ban on parliamentary liaison officers (PLOs) supposedly scrutinising their own bosses.

In her letter, Ms Dugdale said: "Many times you have spoken about the 'new politics' that you believe the SNP and your Scottish Government are bringing to Scotland. However, your Government’s behaviour in proposing the appointment of PLOs to Holyrood Committees in their own portfolio areas flies in the face of this promise.

"I accept that this was something that the last Labour/Lib Dem coalition Government in Holyrood did when we were in power. We were wrong then, as you are wrong now. With significant new powers coming to the Scottish Parliament, we cannot have MSPs who hold a position in the Scottish Government and who receive confidential Scottish Government information scrutinising the Government in their own portfolio areas.

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"I am urging you to reconsider the appointment of PLOs in the interests of ensuring proper scrutiny of your Government, and to reintroduce the ban in the Ministerial code. Failing to do so will make Scottish Parliament committees less independent than those in the UK Parliament and will confirm that the SNP are now beginning to make the same mistakes in power that we once did."

The SNP was once against strongly opposed to ministerial aides sitting on committees at all, with current cabinet minister Fiona Hyslop warning the roles were incompatible as MSPs "cannot serve two masters". However, the party has now systematically extended the practice to every PLO role, with Ms Hyslop's own aide sitting on the Europe committee which she regularly appears in front of.

The party has now adopted an opposite stance to the one it held in opposition, arguing that "in no way" do the roles of PLOs clash with offering scrutiny in committee roles.

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Rules in the ministerial code banning aides from sitting on committees relevant to their boss's brief were quietly dropped by Alex Salmond in 2008, although they remain in force at Westminster.

Under the plan put forward by Ms Dugdale, the ministerial code would be amended to state PLOs should be afforded "as great a liberty of action as possible" but "they should not serve on Committees with a substantial direct link to their minister’s portfolio." They would also not be allowed to ask oral questions of their minister in the Holyrood chamber.

A spokesman for Joe FitzPatrick, the SNP's minister for parliamentary business, said: "The Ministerial Code was updated in 2008 to replace Ministerial aides with Parliamentary Liaison Officers (PLOs) following the formation of a minority administration, and it has been updated twice. 

"The purpose of PLOs is to provide a link between all parties, Parliament as a whole and Government Ministers.  No party holds a majority on any Parliamentary committee and all MSPs are able to fully scrutinise Scottish Government Ministers."