Jeremy Hunt has used official, tax-payer funded, Commons headed notepaper in his Tory leadership campaign against Boris Johnson.
In a letter admonishing his rival for failing to take part in TV debates, the foreign secretary used the portcullis symbol - the emblem of both Houses of Parliament.
The Office of the Parliamentary Commissioner for Standards did not comment on Hunt’s use of headed notepaper.
But the rules governing the use of the portcullis state it should be used by MPs for their “parliamentary functions”.
“It not be used where its authentication of a connection with the House is inappropriate, or where there is a risk that its use might wrongly be regarded or represented as having the authority of the House,” the rules add.
MPs are given a budget for stationery and postage of up to £9,000 a year.
In the letter, Hunt told Johnson: “If you want the job, you have to turn up for the interviews.
“Scrutiny can be uncomfortable. But if we can’t handle it with friends, we won’t deserve to lead against our opponents.”
Sky News today cancelled its planned TV debate after Johnson refused to take part.
The broadcaster had asked Johnson and Hunt to take part in the event on Tuesday night hosted by Kay Burley. It has now invited both men to take part in a debate on July 1 instead.