The Met said it had borrowed 500 officers from other forces for the day, with police vans from Leicestershire, Nottinghamshire and Devon and Cornwall.
There were a mix of slogans on the flags including ‘Stop the Boats’, ‘Send them Home’ and ‘Unite the Kingdom,’ and anti-transgender activists are among the crowds.
One man carried a large wooden cross with ‘RIP Charlie Kirk’ written on it – the right-wing US activist shot dead on Wednesday while speaking at a university.
The rally is set to include speeches from US President Donald Trump’s former strategist Steve Bannon and presenter Katie Hopkins.
Elsewhere, around 500 people gathered near Russell Square for the ‘March Against Fascism’ counter protest organised by Stand up to Racism (SUTR).
Demonstrators held placards reading ‘Women Against the Far Right,’ ‘Oppose Tommy Robinson,’ and ‘Refugees Welcome’.