Theresa May has branded alleged comments made by John Bercow about Commons leader Andrea Leadsom “unacceptable”.

The Speaker reportedly referred to the senior cabinet minister as “a stupid woman” who was “fucking useless” in an angry outburst in the chamber on Wednesday.

A Downing Street spokesperson said if an official complaint is made by Leadsom then it should be “properly investigated by the House”.

“The prime minister has seen the alleged language used and clearly she thinks it is unacceptable,” they added.

Asked if rules and procedures around bullying and harassment in Parliament should be reviewed, Number 10 said there were “a couple of mechanisms in place” to deal with such issues, including an independent investigation currently being carried out by Dame Laura Cox and the cross-party working group chaired by Leadsom herself.

A spokesperson for Bercow – who has also been accused of bullying former staff members – did not deny the remarks had been made.

“Wednesday was an unusual and controversial day in how business was handled in the House by the government and some strong and differing views were expressed on all sides on the subject,” they said.

“The Speaker treats his colleagues with respect and strives at every turn to facilitate the House of Commons.”

Bercow was reportedly angry that the government had used its own statements to eat into Opposition Day debating time.

Leadsom is not believed to have heard the remark herself, but is expected to call for an investigation into the alleged behaviour of the Speaker, who is under increasing pressure to stand down. 

The PM’s spokesperson said she had confidence “in the work that [Bercow] is currently doing” but that decisions on his future would be for the Commons as a whole to make.

“The speaker is elected by MPs, so questions of confidence are for Parliament,” they added.