A Unite the Kingdom march organised by anti-immigrant and anti-Muslim activist Stephen Yaxley-Lennon, also known as Tommy Robinson, is due to meet near London's Waterloo Bridge on Saturday before making its way to the southern end of Whitehall, where a rally will take place.
A counter-protest, organised by Stand Up To Racism, is due to gather at the other end of Whitehall, the main thoroughfare toward parliament.
The Unite the Kingdom march is expected to mourn Charlie Kirk, the American conservative activist shot dead on Wednesday as he gave a talk at a university in Utah.
London's Metropolitan Police said barriers would be in place to create space between the two groups.
It said more than 1600 officers would be deployed across London on Saturday, including 500 brought in from other forces, as the city also hosted high-profile soccer fixtures including West Ham versus Tottenham, concerts and other events.
About 1000 officers will be on duty at the marches.
"We will approach them as we do any other protests, policing without fear or favour, ensuring people can exercise their lawful rights but being robust in dealing with incidents or offences should they occur," said Commander Clair Haynes, who is leading the policing operation.
Almost 900 people were arrested last Saturday at a London demonstration against the ban on the group Palestine Action.
Immigration has become the dominant political issue in Britain, eclipsing concerns over a faltering economy, as the country faces a record number of asylum claims and arrivals by migrants in small boats across the Channel, including more than 28,000 this year.
Facing mounting public criticism over immigration, Prime Minister Keir Starmer last week appointed Shabana Mahmood as Britain's new interior minister in a shake-up of his government.
