The Liberal Democrats have written to cabinet secretary Simon Case asking him to investigate whether the then-prime minister discussed his own financial affairs at the grace-and-favour state mansion.
Mr Johnson used Chequers to host a dinner with BBC chair Richard Sharp and his distant Canadian cousin Sam Blyth – the guarantor for a credit facility of up to £800,000 – in May 2021.
Under the ministerial code, ministers can only use official residences for personal activities if it is paid for at their own expense.
In a letter shared with The Independent, Lib Dem chief whip Wendy Chamberlain asked Mr Case to launch and “urgent” investigation and establish whether the £800,000 credit line was discussed.
“We need urgent clarity over whether Johnson’s used Chequers to discuss his own personal financial affairs, and if so whether he paid the expenses himself,” she said. “Failure to do so would be a potential breach of the ministerial code and an inexcusable misuse of taxpayers’ money.”
The senior MP added: “Boris Johnson’s whole premiership was tarnished by sleaze and scandal. The British people deserve to know whether Johnson used public money to secure his own personal piggy bank.”
Mr Johnson has dismissed the furore as a “load of complete nonsense” – saying he was “ding-dang sure” that the BBC chairman had no knowledge of his personal finances.
Mr Sharp said in an interview with the BBC on Tuesday that the £800,000 credit arrangement did not come up during the dinner at Chequers – saying he only went to “bat” on behalf of the broadcaster.
The chairman has been facing calls to stand down after it emerged that in late 2020 he had introduced Mr Blyth to the cabinet secretary so they could discuss whether the billionaire could act as a guarantor for the credit line.
But Mr Sharp, later appointed BBC chair in February 2021, insisted he would remain in place and was “confident” he had been given the job on merit rather than any favouritism.
The former banker said he had contacted the cabinet secretary to discuss an offer of financial assistance from his “old friend” Mr Blyth for Mr Johnson, before withdrawing from any further discussions.
“I had clarified and agreed with the cabinet secretary, both of us had the judgment that I’d avoided a conflict or a perception of conflict,” Mr Sharp.
Asked how that meeting came about, he said: “Sam came to me and said, ‘Do you want to come to Chequers? I’m going down to have dinner with Al’ [short for Mr Johnson’s first name Alexander].
“I said, ‘Yeah, great’ – I’d never been to Chequers and Sam drove me down and we had dinner and I took advantage of that opportunity to bat for the BBC.”
He added: “I don’t know anything about Boris Johnson’s finances” as that was “between him and his family”.
On Monday, public appointments commissioner William Shawcross announced he is to investigate Mr Sharp’s appointment as BBC chairman in February 2021 to ensure the process was conducted “fairly, openly and on merit”.
Mr Sharp said that he believed his selection was conducted “by the book” and denied he had misled the advisory panel – or MPs on the Commons Digital, Culture, Media and Sport Committee when he appeared before them.
The BBC chairman will be grilled again at the same committee on 7 February to face questions, with acting chairman Damian Green writing to Mr Sharp on Tuesday to invite him to attend.
Former BBC presenter Andrew Marr has called on the BBC chair to resign, saying the story was “toxic” for the broadcaster’s reputation.
“It would be much better for the BBC if Richard Sharp stepped aside, and a new chair could be found who wasn’t party political or so deeply steeped in senior Tory circles,” he said.
Rishi Sunak, under pressure over Tory chairman Nadhim Zahawi’s tax affairs, has sought to distance himself from the Johnson loan controversy, saying Mr Sharp’s appointment was made by “one of my predecessors”.
Meanwhile, Downing Street has said the UK will not dictate to allies what form support for Ukraine should take, after Mr Johnson called on western nations to send more tanks.
Amid pressure on Germany to step up its response, Mr Johnson repeated his call for western countries to send more weapons to Kyiv. “Look at those brave Ukrainians and answer me this question: just what the hell are we waiting for?” the ex-PM wrote in the Daily Mail.