"Experience has shown us that protests such as those planned for this weekend can create tension and disorder," a Met Police Commander said ahead of the rallies.
Supporters of jailed British far-right activist Tommy Robinson — real name Stephen Yaxley-Lennon — will on Saturday afternoon protest in central London to demand his release.
A counter-protest, organised by groups including Stand Up to Racism and Stop Tommy Robinson, will also be held.
London Metropolitan Police have imposed geographic and time conditions on both rallies.
"Experience has shown us that protests such as those planned for this weekend can create tension and disorder, not just on the day itself but in the longer term," Commander Kyle Gordon said in a statement.
Robinson, 36 is the former leader of the English Defence League. He was sentenced to nine months in jail in July over live broadcasting outside a rape trial last year.
The judges at the Old Bailey court in central London said his Facebook Live video had encouraged "vigilante action" and that it breached the reporting restrictions with Robinson "aggressively confronting and filming" some fo the defendants.
Robinson and his lawyer, Richard Furlong, have argued however that he had only provided information that was already in the public domain.
His supporters claim that Robinson is a "political prisoner" and have staged protests in London and Manchester — where he is carrying out his prison term — since his sentencing.
Stand Up to Racism and United Against Racism said on Facebook that they "can't allow Nazis to march through our streets unopposed."
"We face the challenge of taking on increasingly normalised racism from the top of the establishment. The far-right here may be on the back foot after Robinson's humiliations, but it has not gone away," they wrote.
As many as 15,000 marched through central London in a June 2018 rally organised after Robinson was jailed for contempt of court. Five police officers were injured and several protesters were detained.