Caroline Nokes, the immigration minister, is under investigation by the Conservative Party for breaching planning laws and allegedly failing to pay the proper rate of council tax on her constituency home.

The Tories established an inquiry earlier this month after receiving a complaint from a local campaigner in relation to planning works on Nokes’s £1m family home on the edge of the New Forest in Hampshire.

The complaint centres on a planning application to build a set of stables and a double garage, which was submitted in the married name of Nokes’s sister, who was identified as the property’s owner.

The investigation is examining a potential breach of the Conservative Party code of conduct, which states that “holders of public office” should be “truthful” and