The Metropolitan Police has been asked to investigate a man seen wearing a Hamas bandana during a protest outside the Israeli embassy in London on Saturday.
Although no arrests were made during the rally to mark a year since the March of Return protests began at the Gaza border, officers were subsequently sent photos of the man in question.
They were also sent another photo showing a man who appeared to be flying the flag of the Popular Front for the Liberation of Palestine.
It is a criminal offence under the Terrorism Act 2000 to “display an article, such as a flag, in such a way or in such circumstances as to arouse reasonable suspicion that they are a member or supporter of a proscribed organisation”.
A police spokesman said each case depends “on its own particular facts including any supporting evidence”.
He added: “We recognise that activity and behaviour like this can cause concerns within communities. We are committed to disrupting and dealing with any groups or individuals who aim to cause harm or spread fear and hatred, no matter what their ideological or political motive.”
Home Secretary Sajid Javid recently announced that the UK was now proscribing Hezbollah in its entirety, overturning longstanding Foreign and Commonwealth Office concerns that doing so could cut communication channels with a group that comprises part of the Lebanese government.
The full proscription now means that there is no legal loophole for anti-Israel activists to fly the flag of Hezbollah on the streets of the UK, something regularly seen during the annual Al-Quds Day march through central London.