Ms Mordaunt has recently been thrust into the spotlight in the race to become Prime Minister, after stronger-than-expected performances in the first two Tory leadership votes.
She came second place in both rounds - behind former Chancellor Rishi Sunak - outperforming Foreign Secretary Liz Truss, former Levelling Up minister Kemi Badenoch, and Chairman of the Foreign Affairs Committee Tom Tugendhat.
This has resulted in attacks from Tory MPs on the right of the party, most of whom are backing Ms Mordaunt’s rival Ms Truss.
Former Brexit minister Lord Frost - who has announced his support for the Foreign Secretary - launched the most scathing one.
But who is Lord Frost, and what exactly did he say about Ms Mordaunt?
Who is Lord Frost?
David Frost is a former diplomat, civil servant and politician.
He was appointed the UK’s Chief Negotiator for Exiting The European Union by Boris Johnson during the 2019 Brexit negotiations.
Lord Frost helped bring about the revised Brexit withdrawal agreement, before leading the UK’s negotiations with the EU on a free trade agreement during the Brexit transition period.
On 31 January 2020, Lord Frost was appointed Chief Negotiator of Task Force Europe.
He was replaced a year later by Ms Truss.
Lord Frost was introduced to the House of Lords as a peer on 8 September 2020, later appointed UK Representative for Brexit and International Policy.
In March 2021, he was made a Minister of State at the Cabinet Office, and given responsibility for both the domestic and international aftermath of Brexit.
He resigned on 18 December 2021, stating he had “concerns about the current direction of travel” of the Government.
What did he say about Penny Mordaunt?
In an interview with TalkTV, Lord Frost claimed he had “grave reservations” about Ms Mordaunt becoming Prime Minister.
He criticised her capability when carrying out exit talks with the EU, stating, “I felt she did not master the detail that was necessary in the negotiations last year. She wouldn’t always deliver tough messages to the EU when that was necessary.”
The Brexit hardliner continued: “She wasn’t fully accountable, she wasn’t always visible. Sometimes I didn’t even know where she was.”
Lord Frost then claimed that he asked the then-Prime Minister Boris Johnson to remove Ms Mordaunt from the team and find someone else to support him.
Ms Mordaunt acted as Lord Frost’s deputy in Brexit negotiations with the EU.
Lord Frost went so far as to say he wouldn’t be able to serve in a ministerial role under Ms Mordaunt.
He said: “The party has made wrong choices in recent years and I want to make sure we make the right one this time, so I had to make my views clear.”
How have other MPs reacted?
Simon Hoare, who is towards the left of the Conservatives, today (15 July) hit back at Lord Frost.
The MP for North Dorset said: “Who the hell is an unelected, failed minister to tell any MP what to do?
“For some unknown reason, David Frost perpetually thinks we give a flying **** what he thinks. We don’t and we won’t.”
Simon Clarke, who has announced his support for Ms Truss as the UK’s next Prime Minister, shared a clip from Lord Frost’s interview on Twitter.
He wrote: “Lord Frost’s warning is a really serious one. @Conservatives - and far more importantly our country - need a leader who is tested and ready.”
What was Penny Mordaunt’s involvement in Brexit?
Ms Mordaunt voted to leave the European Union.
She was one of the leading voices of the “Leave” campaign during the Brexit referendum, and was appointed Lord Frost’s deputy in the UK’s negotiations with the EU.
She has since continued to praise the UK’s departure from the EU, writing in an article for The Telegraph that “the benefits are huge.”
She came under fire during Brexit campaigns however when she falsely claimed the UK would have no say in whether Turkey could join the EU.
In a recent interview with LBC, Ms Mordaunt backed her remarks, commenting: “I actually stand by that. Well, the short answer is the British public didn’t have a say. The long answer is it was government policy.”
She continued: “There is a provision for veto, but we could not have used it.”