The newly promoted Education Secretary came under pressure over her links to Opus Dei from Tom Sackville, a former Conservative minister who chairs Family Action and Information Resource, a support group for cult victims.
The organisation had many complaints from families who had “lost” their children to Opus Dei, which made members pay it up to 80 per cent of their salaries, he said.
“Of all the Cabinet posts an Opus Dei member could hold, Education Secretary is the most dangerous because the main problem with the cult is their recruitment of young people at colleges and universities.”
Mr Sackville was unseated in his Bolton West constituency by Mrs Kelly – but he insisted that his criticism of her was “not sour grapes”.
He said he had campaigned against cults as a Home Office minister in John Majorís government and tried unsuccessfully to strengthen the policy against them.
He said: “Ruth Kelly is a very competent politician and very well educated.
“But nobody in high office who is also a member of a cult is stable enough to make government policy.”