Met Police Deputy Assistant Commissioner James Harman said the policing operation will cost the force £4.5m.
The Met said the risks from the protests meant it had to impose the “highest degree of control”, including the first use of live facial recognition cameras as part of a protest policing operation.
Live facial recognition is being used at Euston and King’s Cross St Pancras railway stations, where people attending the Unite the Kingdom march are likely to arrive.
The Met said officers had arrested two men near Euston station. They were wanted on suspicion of GBH following an incident in Birmingham, and were spotted arriving in London to attend the Unite the Kingdom rally.
Drones are being used to monitor both protest routes, while officers in Wembley will also monitor CCTV feeds from the FA Cup final to identify supporters travelling towards demonstrations.
Eleven foreign “far-right agitators” have been blocked from entering the country to attend the Unite the Kingdom event, the government said on Friday.
Among the 11 blocked from entering the UK is the US-based, anti-Islam influencer Valentina Gomez, who attended the first Unite the Kingdom march last September.
In a statement on Friday, Sir Keir Starmer said: “We’re in a fight for the soul of this country, and the Unite the Kingdom march this weekend is a stark reminder of exactly what we are up against.
“Its organisers are peddling hatred and division, plain and simple. We will block those coming into the UK who seek to incite hatred and violence.
“For anyone who sets out to wreak havoc on our streets, to intimidate or threaten anyone, you can expect to face the full force of the law.”
In a post on X on Saturday morning he added: “Today the voices of division will be loud. They don’t speak for the country I know, one that belongs to all of us.
“That’s our Britain. A Britain worth fighting for.”
Ahead of the march, Robinson, whose real name is Stephen Yaxley-Lennon, wrote in a post on X: “Today, we Unite the Kingdom and the West in the greatest patriotic display the world has ever seen.
“The establishment has shown their hands early, and clearly don’t want the people united. Tough! It’s happening!”
There are strict controls on where the marches can go and and what time they must finish.
Protesters attending the Unite the Kingdom march are due to gather in Kingsway before heading to Whitehall and a rally in Parliament Square.