A fifth of Whitehall’s non-executive directors appointed to oversee the work of government departments have “significant political experience or party alignment”, according to new evidence that ministers are using the posts to bolster their own support.

It comes as demands grow for a complete overhaul of the appointment of Whitehall’s army of non-executive directors (Neds), who have come in for greater scrutiny since Matt Hancock, the former health secretary, was found to have appointed his aide and lover, Gina Coladangelo, to the role at the Department of Health and Social Care last year.

Coladangelo has since left the post following the public exposure of their affair. However, Hancock’s decision to appoint her highlighted the fact that ministers across Whitehall have appointed figures known to be close to them personally. Neds are meant to scrutinise both ministers and their department as part of the role, but there are concerns that they are increasingly being used to bolster ministers and effectively act as special advisers.

About 20% of the 94 non-executive directors currently in post have political experience or allegiances, according to a new analysis by the Institute for Government (IfG) thinktank. It called for a complete overhaul of how they are appointed. Under current rules, their appointments are not regulated in the same way as other senior Whitehall posts, “making it impossible to know whether candidates are genuinely being appointed on merit, or if advantage is being given on grounds of political affiliation”.

Of the 19 Neds identified as having significant political experience or ties, the analysis found 15 exclusively supported the Conservatives, while two – Tory donor Ben Goldsmith and former Conservative and Ukip MP Douglas Carswell – have campaigned for the Conservatives alongside other parties, and one, Gisela Stuart, worked with Conservative politicians on the Leave campaign. 

The government’s fracking tsar has quit the post after just six months, claiming policy relating to the controversial process means there is “no purpose” to her job.

Natascha Engel told the business secretary, Greg Clark, that developing the industry would be “an impossible task” despite its “enormous potential”. In her resignation letter, she said environmental activists had been “highly successful” in encouraging the government to curb fracking.

Engel, a former Labour MP, wrote the letter following two weeks of protests by the Extinction Rebellion group, which brought parts of London to a standstill with demands to cut emissions to zero by 2025.

She wrote: “A perfectly viable and exciting new industry that could help meet our carbon reduction targets, make us energy secure and provide jobs in parts of the country that really need them is in danger of withering on the vine – not for any technical or safety reasons, but because of a political decision.”

Engel complained that a traffic light system that halts fracking when a tremor with a magnitude of 0.5 is recorded “amounts to a de facto ban”.