Thousands of anti-war protesters gathered in central London to hear Jeremy Corbyn alongside other speakers sounding the alarm over the “unmistakeable nuclear threat” of the conflict in Ukraine.

Some members of the crowd – which included Russian, Polish and Lithuanian expats – wept as they voiced fears for those affected by the Russian invasion and its potential escalation.

Demonstrators waved Ukrainian flags and banners reading “Putin = Hitler” and “Putin in the bin” as they marched from outside the BBC’s Broadcasting House to Trafalgar Square on Sunday.

The former Labour leader was among speakers on the podium to call for an end to military action, branding Russia’s partial ceasefire purporting to allow for humanitarian corridors out of Ukraine as “cynical”.

“If you can have a ceasefire for humanitarian corridors for people to be evacuated from certain cities in Ukraine, obviously it’s better if people are evacuated than killed, but it’s so cynical. If you can agree a ceasefire to take civilians out, then agree a ceasefire to stop the war,” he said.

“Unless this war is stopped very quickly it will degenerate into a global conflict between nuclear armed power blocs in which there will be no, no, no winners, only millions and millions of losers.”

The MP, who is now an independent, also said reports of discrimination against people from African and Indian backgrounds on Ukraine’s borders had “utterly shocked” him.

“I cannot be the only person in this square who was utterly shocked when I heard that African students were pushed off trains to make way for somebody else. That Indian students were denied access at the border into Poland and other places.”

He took aim at the UK Government’s “appalling” borders bill as he called for refugees from Ukraine and elsewhere to be welcomed into the UK on a larger scale.

“The Government needs to abandon its appalling Borders and Nationality Bill which would criminalise people for helping refugees… We support refugees, whoever they are, wherever they are, wherever they’ve come from,” he said.

Writer Victoria Brittain said: “At this time we really need to be together. We’re meeting at a moment of terrifying existential crisis – a nuclear war and a climate crisis.”

“Every day of this war with its unmistakeable nuclear threat and its massive fossil fuel consumption intensifies those twin crises,” she added.

“This war can only end in negotiations. A ceasefire, the withdrawal of Russian troops, and a settlement very different from the Treaty of Versailles when the humiliation of one country led to the rise of a despotic mass murderer and World War II.”

The rally was held by the Stop the War Coalition along with the Campaign for Nuclear Disarmament (CND), No to Nato network, and Codepink.

Stop the War has caused controversy in recent months for its Nato-critical stance. It has described itself as opposed to the British Government’s “aggressive posturing” and the bloc’s “eastward expansion”.

Sinn Fein MP Chris Hazzard said: “The thought of Europe sliding once again into the perilous wars of the past is horrifying and what we actively oppose.”

“Withdraw the Russian troops and return to the negotiation table,” he added.

Elsewhere in the capital, campaigners unfurled an 18-metre Ukrainian flag calling for solidarity with the country’s citizens and refugees.

The stunt, organised by Freedom From Torture, was carried out on Westminster Bridge with Parliament and Big Ben in the background.

Chief executive Sonya Sceats said it was intended to send a clear message to Government that its borders bill would “penalise Ukrainians who make their own way to the UK”.

“They are ignoring the public (support for those fleeing the conflict) – so we put this message where they couldn’t possibly miss it,” she said.

And a separate protest in support of Ukraine was held in Parliament Square and also attracted hundreds of supporters.

Many waved Ukrainian flags while others held signs with messages including “Sanctions don’t stop tanks,” “Close the airspace over Ukraine” and “Say no to dictators”.

Protesters also gathered in Bristol town centre to rally against the invasion, many of them wearing the yellow and blue of the Ukrainian flag.

Andrew Warsley, 76, who attended with his band, told the PA news agency: “I’m very concerned about what Putin is doing and where the consequences could be going.

“The UK could be doing more – we don’t want to get into a war with Russia but we could do with putting Putin under a lot more pressure.

“I’d like to see us stopping all Russian oil and gas imports.”

Josh Pysanczyn, 26, a research scientist, said he had relatives in Ukraine who were “standing their ground” against the assault.

Alison Lochhead, 68, said: “A lot of people will die but more people will die if there’s a nuclear war.”