Conservative MP Miriam Cates has been placed under investigation by Parliament’s standards watchdog.

The backbench MP is facing claims that she has caused “significant damage to the reputation of the House as a whole, or of its members generally”, according to the Parliamentary Commissioner for Standards.

It is not known what the investigation relates to.

The details of investigations by the Standards Commissioner, Daniel Greenberg, are kept confidential until the inquiry is concluded and those under investigation are barred from discussing the allegations.

Ms Cates was elected as MP for Penistone and Stocksbridge in 2019 and has become a leading figure of the right-wing New Conservatives group alongside fellow backbencher Danny Kruger.

The group includes mostly MPs elected in 2019 and has called for tax cuts, significant cuts to immigration, and withdrawal from the European Convention on Human Rights.

The New Conservatives has also provided financial support for a number of Tory MPs, donating £5,000 each to the campaigns of Jack Brereton, Mark Jenkinson and Marco Longhi in the past month.

In 2021, Ms Cates and Mr Kruger also established the New Social Covenant Unit (NSCU) to promote “families, communities and the nation”.

Earlier in 2023, the NSCU published a review commissioned by Ms Cates criticising sex education and claiming children were being shown inappropriate material, prompting Prime Minister Rishi Sunak to order a review of guidance on the subject.

Teaching unions in turn denied Ms Cates’ claims, saying there was “no evidence to suggest there is a widespread problem” and calling the review “politically motivated”.

A former science teacher, Ms Cates has become a fixture at right-wing conferences, addressing the National Conservatism conference in May and the Alliance for Responsible Citizenship conference in October.

She has been outspoken in her concern about declining fertility rates in Britain, calling for policies to promote marriage and having children.

She is one of eight MPs currently being investigated by the Standards Commissioner, all Conservatives or former Conservatives.

These include Deputy Speaker Dame Eleanor Laing, Sir Bernard Jenkin and Virginia Crosbie, who are believed to be under investigation for allegedly attending a birthday drinks event in breach of lockdown rules.

The Metropolitan Police closed their investigation into the same allegations on December 8 with no action being taken against any individuals.

Other Conservative MPs under investigation include Bob Stewart, Marco Longhi and David Duguid, with former Tory Andrew Bridgen, who now sits as a Reclaim Party MP, also the subject of an inquiry.