Tens of thousands of people have gathered in London to march against the far right in the biggest multicultural demonstration in UK history.

Organisers claimed half a million people had travelled to the capital for the Together Alliance march. Police estimated the turnout closer to 50,000, although they admitted it was difficult to judge due to how spread out the crowd was.

Beginning in Park Lane, more than 100 charities, campaign groups and trade unions marched to Trafalgar Square via Whitehall in a show of unity against far-right politics.

The protest was in response to Tommy Robinson’s “unite the kingdom” rally in September, when 110,000 people marched through central London.

The event was supported by a wide range of celebrities, including the actors Christopher Eccleston, David Harewood, Lenny Henry, Steve Coogan, Toby Jones, Lolly Adefope and Maxine Peake, the musicians Paloma Faith, Charlotte Church, Brian Eno and Beverley Knight, and the comedian James Acaster.

Dozens of coaches had arrived from all over the country, including 10 from Manchester alone.

Demonstrators saw performances from Self Esteem, Jessie Ware, Katy B, Joy Crookes, UB40 and Hot Chip.

Speeches from the Labour MP Diane Abbott and the Green party leader, Zack Polanski, attracted roars from the crowd gathered on Whitehall.

Polanski told the crowd: “Go back to your communities, to the community centres, to your trade unions, to your friends, to your neighbours.

“We must organise in our communities. Local elections are coming in just a few weeks’ time,” he added.

“We will defeat hate. It’s time to make hope normal again.”

Attenders brought out some of their best costumes, including Jesus and the grim reaper.

Woody, part of a group called Cut the Ties to Fossil Fuels and dressed in the grim reaper costume, told the Guardian he had come “dressed as Big Oil”.

“Big Oil are one of the major funders of Reform UK,” he said. “We’re here to make that link that we need to cut the ties to fossil fuels.

“Big Oil’s tentacles reach across through many industries, and it’s those enablers of the fossil fuel industry that, as a movement, Cut the Ties to Fossil Fuels, target.”

He added: “I’m mid-fifties now, and I hear people talking about left and right in a way that I haven’t heard since I was in school.”

He said it was important to unite on the left and work together, which is something the right tend to do well “despite having massive differences”.

“It’s a numbers game in a way. This is really important to send a message. So I’m really excited about being here today and being part of a much bigger thing.”

Plenty of other environmental groups were also present. The red rebels, from Extinction Rebellion, walked silently in the opposite direction to the march with white painted faces and red robes. They said they were drawing attention to the climate crisis.