Boris Johnson’s sister has suggested that Cabinet Secretary Simon Case was central to the then-prime minister’s arrangement of an £800,000 credit facility.

It comes as Labour has asked for an investigation into the appointment of BBC chairman Richard Sharp amid claims he helped Mr Johnson secure a loan – weeks before the then-PM recommended him for the role.

Rachel Johnson denied any knowledge of her brother’s financial affairs before reports emerged in The Sunday Times.

Cabinet Meeting
Boris Johnson looks on as Cabinet Secretary Simon Case gestures at a Cabinet meeting at 10 Downing Street in 2022 (Carl Court/PA)

She told the BBC’s Sunday With Laura Kuenssberg programme: “All the parties involved have given statements to The Sunday Times, which suggest they did everything above board and everything was transparent.

“I suggest you ask Simon Case, who seems to be the linchpin in both these stories, to come on and say what happened.”

According to The Sunday Times, Mr Sharp introduced multimillionaire Canadian businessman Sam Blyth – who proposed to act as Mr Johnson’s guarantor for a credit facility – to Mr Case.

The newspaper said Mr Johnson, Mr Sharp and Mr Blyth then had dinner at Chequers before the loan was finalised, though they denied the then PM’s finances were discussed.

Mr Sharp, a former Goldman Sachs banker, was announced as the Government’s choice for the BBC role in January 2021.

Mr Case was appointed Cabinet Secretary and head of the Civil Service in September 2020 following a shake-up under Mr Johnson and his chief adviser Dominic Cummings.

Previously, Mr Case spent nearly two years as the private secretary to the then-Duke of Cambridge before temporarily moving to Number 10 in May 2020 as a permanent secretary to assist with the coronavirus response.

Before taking up his duties at Kensington Palace in 2018, Mr Case was one of the UK’s lead officials working on the border issues between the Republic and Northern Ireland created by Brexit, during his term as the director-general Northern Ireland and Ireland in the Department for Exiting the EU.

In March 2017, he was appointed director-general at the UK Permanent Representation to the EU for the UK-EU Partnership, a role which saw him lead “the UK Government’s work on exiting and seeking a new partnership with the European Union”.

He also served as principal private secretary to David Cameron when he was prime minister and to his successor Theresa May.

A doctor of philosophy, the Cambridge-educated Mr Case joined the Civil Service in 2006 and was director of strategy at the intelligence and security organisation GCHQ from 2015 to 2016.

His promotion to Cabinet Secretary came after Sir Mark Sedwill announced he would step down from the post amid reports of clashes with Mr Cummings.

Mr Case is the youngest Cabinet Secretary since 1916 and is reportedly younger than all permanent secretaries bar one, according to The Times newspaper.