The Labour peer Baroness Morgan of Huyton accused David Cameron of secretly trying to pack public bodies with Conservative Party supporters.
Her claims come as she was told she would not be appointed for a second three-year term as the chairman of the schools inspectorate, Ofsted.
"I am the latest of a fairly long list of people now who are non Conservative supporters who are not being re-appointed. I think there is absolutely a pattern. It's extremely worrying," she told the BBC Radio 4 Today programme.
Lady Morgan, who has agreed to stay on until the autumn while a successor is found, stressed she had not had any falling out with Education Secretary Michael Gove, and that the impetus behind the appointments appeared to come from No 10.
"There is a lot of concern about it. Often they are people who have been working really well with their organisations and, indeed, with their host departments, so I do think this is coming from No 10. I don't think it is coming from individual departments," Lady Morgan added.
More top news
Scientists have discovered the world's deepest fish with wing-like fins and an eel-like tail during research in the depths of the Pacific.
The tranquil district of Hart has been crowned as the place with the best quality of life in the UK for the fourth year in a row.
Britain's immigration system is in 'critical condition' according to the chair of the Home Affairs Select Committee.