Police in London are under strain over cell space after more than 680 arrests were made during a week of climate change protests by Extinction Rebellion.
In a week of disruption in the capital, climate change protesters have glued themselves to trains, blocked major roads and bridges and protested at Heathrow Airport.
Extinction Rebellion (XR) has pledged to continue causing disruption until its demands, including the Government declaring a climate change emergency, are met.
Scotland Yard has condemned the ongoing disruption and has now warned that arrests made during the week are putting police resources under strain.
"Since Monday, we have made over 680 arrests and of course that places a logistical problem on, and not just, the police service for cell space but also the wider criminal justice system," the force said.
"One thing that is unusual about this demonstration is the willingness of those participating to be arrested and also their lack of resistance to the arrests."
In a further warning to demonstrators, who remain camped on Waterloo Bridge, it adds: "We continue to liaise with the protesters - if you want to protest go to Marble Arch.
"There are conditions imposed on the other locations and you will be arrested."
The warning comes after police towed away the group's pink boat from Oxford Circus on Friday evening after it had blockaded the busy junction for five days.
The mast was dismantled behind a police cordon and the boat was towed away to a nearby location as the climate change protesters chanted, "we have more boats".
Hours earlier Dame Emma Thompson, the Oscar-winning British actress, arrived in Oxford Circus and gave a speech to crowds from the boat.
She said: "We are here in this little island of sanity and it makes me so happy to be able to join you all and to add my voice to the young people here who have inspired a whole new movement."
Speaking after to reporters, Dame Emma added: "If you can't have fun whilst saving the planet, what's the point?
"Protest should always have a sense of joy in it because what we are protesting about is saving this extraordinary home of ours and also celebrating the passion and inspiring energy of this young generation."
Earlier, on Friday morning, about 20 activists, most of them under 17, had staged a brief demonstration on roads near Heathrow Airport.
Standing close to a tunnel which leads to terminals two and three, they unfurled a black banner with the message: "Are we the last generation?"
Waterloo Bridge has now been blocked by demonstrators for six days.