Husam Zomlot, the Palestinian ambassador to the UK, shared a video on X, showing the flood of people into the London streets.
More than 1,000 police officers were deployed to ensure safety and orderly conduct during the demonstration.
UK Home Secretary Suella Braverman issued a warning to police chiefs Tuesday regarding the display of Palestinian flags on British streets.
She suggested that waving the flag "may not be legitimate" if it is seen as a show of support for terrorism.
Braverman said although there are valid reasons for expressing solidarity with Palestinians, certain actions go beyond the boundaries set by the Terrorism Act and the Public Order Act.
She provided examples of protest actions she believes could potentially constitute public order offenses, including targeting Jewish neighborhoods, waving pro-Palestinian or pro-Hamas symbols, and chanting slogans that could be interpreted as anti-Israeli.
