After marching through Oxford Circus and Regents Street, the crowd gathered in a packed Parliament Square to hear the Labour leader and other politicians and union leaders speak.
Protesters carrying banners and placards, many of which focused on the Grenfell Tower disaster and cuts to public services, sang the now infamous “Oh Jeremy Corbyn” chant as they marched.
Corbyn told the crowds in Westminster: “We are the people, we are united and we are determined, we are not going to be divided or let austerity divide us. We are increasing in support and we are determined to force another election as soon as we can.”
Corbyn also rounded on the Tories for this week raising hopes the public sector pay cap would be lifted, before later voting against a Labour amendment to the Queen’s Speech to scrap the 1% ceiling.
In reference to the Tories’ deal with the DUP, he said: “I say to any public sector workers in Northern Ireland or anywhere else – don’t have any illusions in these people, when they started the austerity programme they meant it and they meant it to carry on and carry on.”
He then went on to slam the “hypocrisy” of Tory MPs who praised the work of the emergency services dealing with Grenfell Tower and the recent terror attacks.
“The utter hypocrisy of government ministers and others who queued up in the chamber over there in the House of Commons to heap praise on the emergency services, the following day to cut their wages by refusing to lift the pay cap,” he said. “The hypocrisy is absolutely unbelievable.”
Earlier, the anger and rising tensions in the weeks since the general election and the Grenfell blaze appeared to give way to a carnival atmosphere, with people blowing whistles while percussionists and other musicians joined in.
When the march reached Parliament Square, a minute’s silence was held “in memory and respect” to the victims of Grenfell Tower. Tributes were also paid to the emergency services who responded to the fire with a minute’s applause.
He said: “To the victims of Grenfell Tower we pledge now, we will stand with you and your families all the way through. We bring you sympathy but more importantly we bring you solidarity.
“We will not rest until every one of those families is properly housed within the community in which they want to live. Grenfell Tower symbolised for many everything that’s gone wrong in this country since austerity was imposed upon us.”
He slammed the Tories for praising the emergency services “every time there’s a tragedy” but then cutting jobs and wages.
McDonnell will be joined by Corbyn, as well as union leaders Len McCluskey and Frances O’Grady. Diane Abbott, the shadow home secretary who took a break for health reasons during the election campaign, was also at the event.
Protesters gathered outside BBC Broadcasting House in Portland Place on Saturday morning, where speakers included Owen Jones and Abbott, the MP for Hackney North and Stoke Newington.
One protester Nick Packham, who travelled up from Brighton said he was marching for every nurse, doctor, firefighter, teacher and council worker, as well as for the sick and disabled.
“I don’t agree with what Theresa May has done to secure her place at number 10 and it’s at the expense of our public services, the emergency services and the sick and vulnerable in our society,” he said.
Of the atmosphere, he said: “It’s a really good-natured and excited crowd.”
Flora Swane, another protester who works in the voluntary sector and came with her sister, agreed: “The atmosphere has been really positive with no violence,” she said. “This is the first demonstration I’ve been to, and it’s been really inspiring. There have also been some really moving speeches about Grenfell Tower.
Swane is a supporter of Corbyn and was “proud to see how many new people he’s brought to politics”.
“Members of my family rely on disability and carers’ benefits and I have witnessed first-hand the impact of austerity on those who are most vulnerable.”
She added: “The demonstration has made me more determined to be politically active and ensure we have a Labour government.”
Sarah Davies, a midwife of 35 years who now teaches student midwives, said: “I am here because I am utterly opposed to the Tories’ lies on austerity and attempts to divide people and scapegoat and harm the most vulnerable.
“I work with pregnant refugee women who amaze me with what they have to offer. I can’t bear to see the braying public school lot who really do not care about humanity, pulling apart the NHS as they sell it off to their friends.
The damage austerity is doing breaks her heart, she said. “Midwives and public sector workers are skilled, caring people and the attack on the public sector is massively damaging to them and the care they manage to give despite cuts, short staffing, and the marketisation of the NHS.
“[It is] utterly vile. But I think people are realising another world is possible,” Davies added.
Demonstrators are using the hashtag #notonedaymore on Twitter to publicise the event which has been organised by the People’s Assembly Against Austerity. In a statement on Facebook, the group said: “On Saturday 1 July we invite everyone – from campaigns and community groups across the country, from the trade unions, from political parties, and any individual – to come together in one massive show of strength and solidarity.
“We’re marching against a government committed to austerity, cuts and privatisation. We’re marching for a decent health service, education system, housing, jobs and living standards for all.”
This article was written by Jamie Grierson and Nicola Slawson, for theguardian.com on Saturday 1st July 2017 17.44 Europe/Londonguardian.co.uk © Guardian News and Media Limited 2010