A SENIOR cabinet member loudly railed against allowing junior MSPs to serve as both Holyrood committee members and ministerial aides, only to fully embrace the practice after entering Government.

Fiona Hyslop, the Culture and External Affairs Secretary, once claimed that it was damaging for MSPs to sit on committees at the same time as being parliamentary liaison officers (PLOs) to cabinet members, as it would compromise their task of providing scrutiny to government.

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During Holyrood's first session, she warned "one cannot serve two masters. One cannot be a ministerial parliamentary aide and serve on a committee" and emphasised the SNP's "strong opposition" to aides sitting on the groups.

However, Nicola Sturgeon has handed a string of junior MSPs jobs as assistants to the same cabinet member they are expected to hold to account in their committee sessions. The move sparked anger among opposition parties and has been branded a "stitch up" designed to weaken parliament.

Ms Hyslop's assistant, Ashten Regan-Denham, was picked for the job after she won a place on the Europe committee, which regularly calls the minister as a witness. The pattern is repeated across every cabinet brief, with, for example, education secretary John Swinney's aide sitting on the education committee and finance secretary Derek Mackay's on the finance committee.

The SNP has insisted that "in no sense" do the responsibilities of PLOs clash with the role of scrutinising Government through committees, and attacked "hysterical" criticism from opponents.

But speaking in 2002 after Labour moved to place former MSP Elaine Thomson, then aide to the enterprise and transport minister, on the loosely-connected local government committee, Ms Hyslop blasted the move.

She said: "It is inappropriate for a ministerial parliamentary aide to sit on a committee that scrutinises the Executive. The appointment of a ministerial parliamentary aide is under the patronage of the First Minister, so the aide is beholden to the Executive."

Ms Hyslop went on to cite the Scottish ministerial code, which then banned PLOs from sitting on committees directly tied to the brief of the minister they served. The rule was quietly scrapped by Alex Salmond after the SNP won power in 2007.

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She added: "That is why the Scottish National Party objects so strongly to the appointments of ministerial parliamentary aides in the first place but, more important, objects to those aides joining committees. To do so undermines the committees' independence, which is so vital to Parliament.

"We must preserve the committees' integrity and their ability to scrutinise the Executive. One cannot serve two masters. One cannot be a ministerial parliamentary aide and serve on a committee."

At Westminster, the equivalent of PLOs - parliamentary private secretaries - are banned from making any contribution linked to the minister or department they work for. However, at Holyrood the posts have been handed to MSPs with committee roles directly tied to the boss's policy area.

It leaves cabinet members with an insider on the committees, which can quiz ministers, amend legislation, launch enquiries and issue potentially damning reports, that could cause them the most difficulty.

Mike Rumbles, the Liberal Democrat MSP, said the public deserved committee members relentless in questioning ministers, rather than "cheerleaders". The party could demand a new vote on committee membership, which was approved by Holyrood before PLOs were publicly announced.

Labour's business manager, James Kelly, said the move was "typical of the SNP's arrogant approach to government" and should be reversed. Tory MSP Alex Johnstone said: "We need a parliament with teeth, not one hobbled by SNP cronyism."

The SNP rejected the criticism. A party spokesman said: "The latest hysteria from opposition parties is more a case of political bandwagonism than honest concern – PLO and committee appointments have of course been a matter of public record for months, and the system itself has been in place for years.

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"PLOs support Scottish Ministers in maintaining a positive and constructive relationship between the Scottish Parliament and Scottish Government – something which we would have thought these opposition MSPs would welcome."