In a letter on Tuesday, Home Secretary Suella Braverman called on police forces to be alert for displays of Hamas flags or logos or other demonstrations of support for the Palestinian group.
Hamas was proscribed as a terrorist organisation by the UK government in 2021.
But Braverman also called on police to consider the context in which Palestinian flags are waved to assess whether public order offences of harassment or incitement may have been committed.
“Behaviours that are legitimate in some cricumstances, for example, the waving of a Palestinian flag, may not be legitimate such as when intended to glorify acts of terrorism,” she wrote.
She also encouraged police chiefs to consider whether chants like “From the river to the sea, Palestine will be free” should be “understood as expression of a violent desire to see Israel erased from the world” and therefore a public order offence.
Her comments came hours after British Prime Minister Rishi Sunak vowed that anyone in the UK supporting Hamas in the wake of its “barbaric acts of terrorism” would be held accountable.
“People should not be supporting Hamas and we will make sure that we hold people to account if they are,” he told reporters during a visit to Staffordshire on Tuesday.
The UK government is among a group of countries also including the US, Germany and France who have offered Israel “steadfast support” in the aftermath of a weekend attack by Palestinian fighters from Gaza in which more than 1,200 Israelis are reported to have been killed.
At least 950 Palestinians have been killed as Israel responded with air strikes in Gaza.
On Monday evening, thousands of protesters gathered outside the Israeli embassy in London, waving Palestinian flags and chanting “Free Palestine”.
London police reportedly arrested three people involved in the demonstrations.
Across town, thousands of people attended a Jewish community vigil outside Downing Street while Sunak was at a prayer service at a synagogue in north London.
Over the weekend, Braverman tweeted that she expected police to “use the full force of the law” against any displays of support for Hamas, a message which she reiterated on Monday.
“There is no place on British streets for demonstrations that glorify terrorism. I am writing to police chiefs urging them to use all their powers to prevent disorder & distress,” she posted.
The British government proscribed Hamas in its entirety as a terrorist organisation in November 2021, meaning that anyone who expresses support for the Palestinian group could face up to 10 years in prison.
Previously, only Hamas’s military wing, the al-Qassam Brigades, had been proscribed in the UK.
Earlier this year, a contentious review of the UK goverment’s Prevent counter-extremism strategy recommended that supporters of Hamas should be treated the same as supporters of the Islamic State group.
People in the UK have previously been prosecuted for displaying flags or wearing t-shirts with the logos of proscribed organisations including the Kurdistan Workers’ Party (PKK) and Hamas.
In 2021, a man was convicted but spared prison for wearing t-shirts supportive of the al-Qassem Brigades and the Palestinian Islamic Jihad militant group in a London neighbourhood with a large Jewish population.