Tens of thousands of people are marching through the streets in a rally supporting the rights of refugees.
Protesters will gather in London's Parliament Square where a number of politicians and pubic figures are due to give speeches.
Jeremy Corbyn, the new leader of the Labour Party, is expected to make an appearance.
Liberal Democrat leader Tim Farron and Green Party leader Natalie Bennett are also due to speak.
Musician Billy Bragg, who is performing at the event, said he is "encouraged" by Mr Corbyn's success and added "hopefully this will mean a return to civic culture".
"People are beginning to understand that we do have a lot in common with one another and it's possible to create a society where people's needs are put first," he said.
"The demonisation of people in need that's gone on in this country is not the kind of Britain I grew up in - that everyone who's in need is a scrounger and all refugees are terrorists.
"It's not the compassionate society I want Britain to be seen as around the world."
The protest is backed by the Refugee Council, Amnesty International, the Syria Solidarity Movement, Stand Up to Racism and the Stop the War Coalition.
Organiser Maz Saleem, of Stand Up to Racism, described the Calais refugee camps as "slums" and said "the conditions are absolutely appalling".