Widespread protests are expected against Donald Trump's UK visit but "we will keep him safe", Metropolitan Police Commissioner Cressida Dick has said.
The Metropolitan Police will be responsible for the protection and security of the US president and will also try to ensure lawful protests can be staged.
Ms Dick said: "We will keep him safe. We will facilitate lawful protest and we will uphold other people's rights as much as we can."
She was speaking at the Air Power Conference in London where 450 guests included RAF personnel, foreign air chiefs, academics and industry specialists.
Ms Dick said: "Tomorrow we have some large protests in central London and as the president of the United States makes his way through the country it is the Metropolitan Police who are responsible for his protection and security.
"Tonight there will be protests, tomorrow there will be protests.
"On Saturday there will be sort-of related protests (from the) far-right and far-left and probably the most difficult."
Mr and Mrs Trump arrived in the UK this afternoon and as they landed in Marine One in front of Winfield House, the US ambassador's residence on the edge of Regent's Park, Beatles music was playing the background.
They were accompanied by the US ambassador Woody Johnson as they walked hand in hand towards a large group of people waiting to meet them.
As President Trump's helicopter flew over London, another member of the public showed their distaste for his arrival with a middle finger.
Kate Gleeson filmed herself swearing at the White Hawk over her home in Finsbury Park.