Rishi Sunak may have breached rules by using parliament's Thatcher Room to film leadership campaign video

• Rishi Sunak may have breached rules by using a room on the parliamentary estate for his campaign.
• Sunak booked the Thatcher Room to shoot a film with various MPs saying why they are backing him.

Rishi Sunak may have breached parliamentary rules by using a room on the estate for his leadership campaign, and could face a probe into whether he misused facilities.

The former chancellor, who on Wednesday became one of the last two candidates to succeed Boris Johnson as UK prime minister, gave a celebratory speech in a committee room that was filmed and posted on Twitter.

The video, which includes a large "Ready for Rishi" poster, sees Sunak welcoming and taking photographs with various MPs, several of whom go on to explain why they are backing him.

However, under parliamentary rules, rooms can only be booked for "purposes connected to the parliamentary duties of members or grey passholders… or relevant to the work of Parliament."

Despite Sunak giving his speech to an audience of MPs and aides, the contest had by that point moved beyond Parliament.

The final stage involves seeking the votes of Conservative party members in the head-to-head contest between Sunak and Foreign Secretary Liz Truss. One MP said in the video that he is "looking forward to introducing him to my members".

Insider identified the location as the Thatcher Room – likely a signal to would-be supporters that he intends to channel the former prime minister. The room in the launch video matches archive footage of the Thatcher Room, which is distinctive because of its artwork on the walls.

In a op-ed for The Daily Telegraph, Sunak vowed to be "the heir to Margaret Thatcher", and described himself as a Thatcherite six times.

He is attempting to best rival Truss, who has long tried to project similar parallels, including wearing a virtually identical outfit to one worn by Thatcher during a recent leadership debate.

Sources, given anonymity to speak frankly about the leadership contest, told Insider that the move had provoked outrage among Conservative MPs, as well as MPs from other parties.

One backbencher said it was "careless", while a former minister said the whole process had been "questionable".

The former minister said: "Is the [1922 committee] using room 14 to hold the election connected to parliamentary duties? What about the hustings? All held in committee rooms. It could all be challenged."

Alistair Carmichael, the Liberal Democrat MP for Orkney and Shetland, told Insider: "Using the parliamentary resources for an internal party election looks and feel qualitatively different to party wide meetings to deal with parliamentary business and the rules on this need to be made clearer."

A spokesperson for the Parliamentary Commissioner for Standards Kathryn Stone said: "The House of Commons provides offices to MPs and their staff to enable them to carry out their parliamentary duties.

"Any use of such facilities must be in support of those duties, as specified in the Code of Conduct. Any allegation of misuse of House provided facilities will be taken seriously and may lead to a formal inquiry by the Commissioner."

There is less demand for committee rooms than usual with ministers pulling out of Parliamentary scrutiny sessions.

Kwasi Kwarteng, the business and energy secretary, became the latest to say he could not attend a select committee hearing on Wednesday.

Sunak's team did not respond to requests for a comment at the time of publication.