Pressure is growing on Rishi Sunak to order an investigation into claims Suella Braverman asked civil servants to help her secure a special arrangement after being caught speeding.
No10 confirmed late Sunday that Mr Sunak will consult with his independent ethics adviser, Sir Laurie Magnus, on Monday over the controversy.
He is expected to speak with Ms Braverman, along with Cabinet Secretary Simon Case, upon his return from the G7 summit.
The Home Secretary is alleged to have asked Home Office officials to help organise a one-to-one driving awareness course so she could avoid incurring points on her licence.
Officials refused the request so Mrs Braverman allegedly turned to a political aide to assist her in attempting to arrange an alternative to having to attend a course with other motorists.
Labour’s deputy leader Angela Rayner sought to pile more pressure onto Mr Sunak on Sunday night over the row by setting out a series of questions any inquiry into the allegations should seek to answer.
Labour said Mrs Braverman may have breached the ministerial code if the allegations, first reported in the Sunday Times, are true. It is calling for Sir Laurie to investigate, but he cannot launch an investigation without Mr Sunak's prior approval.
Mr Sunak refused to back Mrs Braverman when asked for his opinion at a press conference in Hiroshima, Japan, where he had been meeting with G7 leaders.
But No 10 has since said he does have full confidence in his Home Secretary, who is likely to face queries about the reports when she comes before MPs at Home Office questions in the Commons on Monday.
In her letter to Mr Sunak, Labour’s Ms Rayner said the Prime Minister should order an investigation “without delay".
She added: “Members of the Cabinet are subject to the same laws as the rest of us, and any attempt to direct civil servants to obtain special treatment in this matter would clearly amount to an unacceptable abuse of power and privilege by the Home Secretary."
Ms Rayner called for the Prime Minister to “show some backbone” and order an ethics probe.
“The public have a right to know whether the minister responsible for law and order sought to abuse her position in an attempt to gain preferential treatment to avoid a speeding fine,” she said.
Her letter also asks whether Mr Sunak knew about the alleged request to civil servants to help her arrange a special course and whether Mrs Braverman informed the Cabinet Office and Home Office permanent secretaries.
In his first speech after entering Downing Street, Mr Sunak vowed to lead an administration with “integrity, professionalism and accountability at every level".
A source close to Mrs Braverman said that she notified the Cabinet Office after being handed the speeding ticket, having reportedly been caught driving too fast on a road outside of London last summer.
A spokesman for the Home Secretary said she regrets speeding and has since accepted the points and paid the fine.
A No 10 source said: “The Prime Minister has always followed the proper process in these matters, and will consult the independent adviser upon his return to London.”
Separately, the Liberal Democrats are calling on Mr Sunak to make a statement in Parliament about the claims surrounding his Cabinet minister.
The party’s chief whip, Wendy Chamberlain, said: “Rishi Sunak is so weak he can’t even make sure his own ministers maintain the very basic level of integrity.
“The least he can do is come to Parliament and explain this farce. After yet another day of Conservative sleaze and scandal, we need to see the Prime Minister take some responsibility."
