Police are assessing a social media post by the wife of the government's national security adviser Jonathan Powell which referenced Palestine Action, a group labelled a terrorist organisation by the Home Office.
Sarah Helm wrote on the social media site X: "God help us authors who support Palestine and Palestine Action."
She was responding to a discussion on Sky News about the author Sally Rooney, whose novels will not be supplied to booksellers in the UK following her announcement that she intends to use her royalties to support Palestine Action.
A No 10 spokeswoman said Helm was "an individual who does not represent the government in any capacity". The BBC has attempted to contact Helm for comment.
On Friday, a Metropolitan Police spokesperson said: "We have been made aware of an X post on Thursday, 15 October referencing Palestine Action.
"It is in the process of being assessed to determine whether any further police investigation may be required."
Reform UK MP Danny Kruger has written to the prime minister raising concerns about Helm's post.
The Campaign Against Antisemitism said the post was "gobsmacking".
"Spouses are entitled to independent views, but plainly Mr Powell, who leads on our country's national security and has been intricately involved in our Middle East diplomacy, must publicly denounce this rhetoric if he is to continue in post," the group said.
However, Green Party leader Zack Polanski said: "Sarah Helm is speaking absolute common sense and should be commended for her bravery."
He called for Palestine Action to be de-proscribed "immediately", calling its official labelling as a terror group "ludicrous and authoritarian".
Helm is an author and journalist, who has previously worked at the Sunday Times and as a foreign correspondent for the Independent.
Palestine Action describes itself as a "direct action movement" that uses "disruptive tactics".
Earlier this year, four of the group's activists were jailed after causing £1.2m of damage at a UK site of an Israel-based defence firm.
In 2025, the UK government proscribed Palestine Action as a terrorist group, saying it would not "tolerate" organisations that put the UK's national security at risk.
The proscription made it a criminal offence to belong to or support Palestine Action, punishable by up to 14 years in prison.
The government's decision triggered a wave of protests, which saw an estimated 3,700 people arrested in the UK for publicly expressing their support for the group.
Around 2,500 have been charged, but the cases have not gone to trial as a legal challenge to the proscription is due to be heard in the Supreme Court next month.
Powell began his government career as a diplomat but later served as an adviser in Tony Blair's government, where he was credited with negotiating a peace deal in Northern Ireland.
In 2024, Sir Keir Starmer appointed him as national security adviser, a position he retained when Andy Burnham became prime minister.