Home Secretary Suella Braverman is facing questions about her future after Downing Street disowned an article in which she accused police of bias.
She claimed aggressive right-wing protesters were “rightly met with a stern response”, while “pro-Palestinian mobs” were “largely ignored”.
She has been accused of undermining the police and is facing calls from some Tories to be sacked.
No 10 said the article had not been approved by Prime Minister Rishi Sunak.
It comes ahead of a Pro-Palestinian march for a ceasefire in Gaza, which is due to take place in central London on Saturday.
Mr Sunak has urged organisers to call the march off because because it coincides Armistice Day, which marks the end of World War One, saying it would be “provocative and disrespectful” to go ahead with it.
The BBC has been told Downing Street had suggested major changes to Ms Braverman’s Times article but not all of them had been applied when it was published.
The prime minister’s spokesperson said Downing Street was “looking into what happened” – but they added Mr Sunak had full confidence in the home secretary.
The ministerial code says all major interviews and media appearances, both print and broadcast, should “be agreed with the No 10 Press Office”.
The prime minister can punish a minister who is deemed to have breached the code. Options can range from demanding a public apology to sacking them.
Sir Keir accused Mrs Braverman of undermining the police and said Mr Sunak was “too weak to do anything about it”.
The home secretary, who is popular on the right of her party and seen as a possible future Conservative leader, often takes a harder line than many of her colleagues on issues such as crime and immigration.
She has recently been criticised for calling pro-Palestinian rallies in London “hate marches” and has described being homeless as a “lifestyle” choice.
This latest row comes before the Supreme Court is due to give its decision on whether government plans to deport asylum seekers to Rwanda are lawful next week.
Ms Braverman has been a vocal backer of the Rwanda scheme, which is part of Mr Sunak’s plans to curb the number of migrants crossing the English Channel in small boats.
Police have said they expect a large rally on Saturday, the anniversary of the end of World War One, prompting fears of violent clashes with counter-protesters.
The force has faced calls to ban the march – but commissioner Sir Mark Rowley protests may only be stopped if there is a threat of serious disorder, and that the “very high threshold” has not been reached.
In her Times article, Ms Braverman claimed that there was “a perception that senior officers play favourites when it comes to protesters”.
“Right-wing and nationalist protesters who engage in aggression are rightly met with a stern response yet pro-Palestinian mobs displaying almost identical behaviour are largely ignored, even when clearly breaking the law,” she added.
There have been regular protests in London after Hamas gunmen launched an unprecedented assault on Israel from the Gaza Strip on 7 October, killing more than 1,400 people and taking more than 200 hostages.
Israel has been carrying out strikes on Gaza since then in response, and has now also launched a ground offensive. More than 10,500 people have been killed in Gaza, according to the Hamas-run health ministry.