Scotland’s opposition parties have reacted with fury after it emerged that SNP ministers’ hand-picked parliamentary aides sit on the same Holyrood committees that are supposed to hold them to account.

The SNP government faced accusations of an outrageous power grab after it was disclosed that Nationalist MSPs appointed as parliamentary liaison officers (PLOs) also sit on the committee covering the same policy area as the minister for whom they work.

For example, Education Minister John Swinney’s PLO, Jenny Gilruth, sits on the education committee and Finance Minister Derek Mackay’s aide, Kate Forbes, sits on the finance committee. The pattern is repeated across every Cabinet brief.

This means ministers who are being cross-examined by a committee over their performance will be questioned by their own PLO, who theoretically could brief them beforehand on the line of questioning that they and other members will take.

Similarly, PLOs could try and discourage the rest of the committee from investigating a particular subject or from asking an expert witness hostile to an SNP policy from giving evidence. They may also have had access to confidential government documents unavailable to their committee colleagues.

The disclosure follows a series of incidents that have raised major doubts over whether some of Holyrood’s committees are holding the SNP government to account. In the absence of an upper house, they are supposed to revise flawed legislation and investigate problems.