Rishi Sunak has refused to order an ethics probe into whether Suella Braverman sought special treatment after getting caught speeding.
The scandal-prone Home Secretary, dubbed "Speedy Sue", repeatedly insisted that "nothing untoward happened" when it emerged that she asked civil servants to enlist her on a private speed awareness course.
But the Prime Minister decided not to sack her or commission a formal investigation into the row after three days of dithering.
Critics blasted the move as a "cowardly cop out" and accused the PM of being ruled by his hard-line backbenchers.
In a letter to Mrs Braverman, Mr Sunak said his independent adviser Sir Laurie Magnus found no "further investigation is not necessary" and he had accepted the advice.
"On the basis of your letter and our discussion, my decision is that these matters do not amount to a breach of the Ministerial Code," the PM said.
"As you have recognised, a better course of action could have been taken to avoid giving rise to the perception of impropriety.
"Nevertheless, I am reassured you take these matters seriously. You have provided a thorough account, apologised and expressed regret.
The row centres on whether Mrs Braverman broke the ministerial code by asking civil servants to enlist her on a speed awareness course - which would be a private matter rather than Government business.
She has since accepted penalty points on her licence and paid the fine.
Her adviser repeatedly denied she had been caught speeding when The Mirror approached her team seven weeks ago - but Mrs Braverman has finally come clean.
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In her letter to the PM, she said she had been caught driving over the speed limit last June when she was Attorney General, and she raised it with her private office when she became Home Secretary in September.
"This reflected my lack of familiarity with protocol relating to my newly acquired official status as a ‘protected person’, which means I am required to have a close protection security team overseeing my movements, and with me always in public," she said.
Her officials raised it with the Cabinet Office who advised it was not an appropriate matter for civil servants to get involved.
She then discussed fears of being covertly recorded doing an online course with political aides but eventually decided to accept the points and pay the fine in November.
She said: "In hindsight, or if faced with a similar situation again, I would have chosen a different course of action.
"I sought to explore whether bespoke arrangements were possible, given my personal circumstances as a security-protected Minister.
"I recognise how some people have construed this as me seeking to avoid sanction —at no point was that the intention or outcome.
"Nonetheless, given the fundamental importance of integrity in public life, I deeply regret that my actions may have given rise to that perception, and I apologise for the distraction this has caused."
Liberal Democrats Chief Whip Wendy Chamberlain MP said: "This is a cowardly cop-out from Rishi Sunak. With every scandal, we see the Prime Minister dither, delay and flip-flop - never taking decisive action.
"This is not the leadership the country needs during such a severe cost-of-living crisis. Sunak is too weak to even order an investigation, let alone sack his Home Secretary.
"Sunak had the chance to do the right thing but instead he's once again chosen to be ruled by his own hardline backbenchers. He may be in office but he is barely in power."
Mrs Braverman has already been forced to resign once for breaching ministerial rules.
In the dying days of Liz Truss's premiership, she was forced out when it emerged she had sent an official document from her personal email to a fellow MP.
But Mr Sunak brought her back as Home Secretary when he became PM days later in a bid to woo the right of the Tory party.
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