The environmental action group Extinction Rebellion marched on Parliament Square today to greet MPs returning from their Easter break.
Extinction Rebellion are rallying to demand that the UK government declare a climate and ecological emergency and go carbon neutral by 2025.
They also want a People's Assembly to be created, to oversee the changes the Government will make.
In their latest action, the group is delivering letters to MPs, inviting them to attend such a gathering.
"What we're having today is a People's Assembly at Parliament Square, where we will be discussing a way forward. People will get together in various groups and look at what we should do next", says Janye Forbes, spokesperson for Extinction Rebellion.
"Everybody asked to get their MP to come out and ... listen and talk about the climate emergency. But now we realise we have been banned from Parliament Square so we have to negotiate with the police", she adds.
This morning, the group gathered at Marble Arch before starting their march to Parliament.
They then started making their way to Parliament Square at around 11:30 this morning and have been updating their whereabouts on twitter.
Below is a tweet from the London Extinction Rebellion account of the protest.
This demonstration is part of an ongoing two-week protest the group has organised - Shut Down London.
Extinction Rebellion calls for a non-violent rebellion against the government.
On their website, they say: "We will be blockading the city, engaging in civil disobedience, taking direct action [...]."
At the beginning of the month, activists disrupted a House of Commons Brexit debate with a semi-naked protest in the public gallery.
This time, the police have prepared for their arrival by increasing security around Parliament.
The police tweeted this morning warning Extinction Rebellion they will only be allowed to protest in Parliament Square Garden, restricting them from going close to Parliament.
They have already arrested more than 1,000 people since the protests started on Monday 15 April. They report having charged 53 people for various offences, including obstructing a highway and obstructing police.
Forbes was one of those arrested last week.
"It's unfortunate that we had to do this. One doesn't really want to spend the entire Easter holiday weekend in a police cell. It's very unfortunate, but it's a step we had to take. They have released us under investigation, so we don't know if we're going to get charged," she told Euronews on Tuesday afternoon.
But she says the police had to arrest them because the group was civilly disobedient.
"They don't have a choice, we were disobeying the law. What we did was illegal. We understood that, they understood that and they arrested us."
On one of their twitter accounts, the Metropolitan Police has also asked the activists to protest lawfully.
Forbes says she does not suspect there will be any more arrests today.
"I have no understanding that the police are looking to arrest at Marble Arch. It's not up to us, it's whether the police decide that it's something that they have to get involved with, and whether we are being peaceful enough that it's not causing public disorder"
"It's also a question of whether or not we be civilly disobedient and go outside of the restricted area, because the MPs aren't going to come across", she says.