A former senior official at the Houses of Parliament has branded the behaviour of Commons Speaker John Bercow "unworthy of someone in such public office".
David Leakey, who retired in 2017 after seven years as Black Rod told the PoliticsHome website that he had personally experienced "intolerable" rudeness from the Speaker.
His comments increase the pressure on Mr Bercow, who is already facing bullying allegations from two former members of his office staff, all of which he strenuously denies.
Downing Street has said that Prime Minister Theresa May regards the allegations as "concerning" and thinks they should be properly investigated.
A spokesman for Mr Bercow's office acknowledged the Speaker had fundamental disagreements in the past with Mr Leakey, who was responsible as Black Rod for maintaining order in the House of Lords, but denied the allegations made by him.
"Mr Speaker refutes all the allegations levelled by Mr Leakey," said the spokesman.
"John Bercow and David Leakey are two very different people with very different backgrounds, perspectives and ideas. They had fundamental disagreements in 2011 and 2012, but interacted adequately after that."
Mr Leakey said that the issue risked bringing Parliament into disrepute unless it was rigorously investigated.
He told PoliticsHome: "His explosive and intemperate behaviour is legendary, objectionable and unworthy of someone in such public office - conduct which may not stand up to the standards expected in public life. There were lots of people who were, frankly, terrified of the Speaker."
Mr Leakey said that on one occasion when "the red mist suddenly descended", Mr Bercow had erupted into a rage, banging the table and making extremely rude remarks to him.
"It was quite disproportionate and unreasonable by any standards," he said.
Mr Bercow is already facing calls to quit following bullying allegations from former private secretaries Angus Sinclair and Kate Emms.
An inquiry is already under way under Dame Laura Cox QC into claims of bullying by MPs. But its remit does not extend to looking at historical cases, including allegations against Mr Bercow.
Leader of the Commons Andrea Leadsom said on Wednesday it was for Dame Laura to consider whether the terms of her probe should be expanded "to allow for individual investigations to take place".
And Downing Street suggested that allegations against Mr Bercow could be considered by the judge-led inquiry, by the House authorities or by the parliamentary Standards Commissioner.