Jeremy Corbyn gave an impromptu speech to hundreds of Labour supporters who had appeared outside the Question Time venue, cheering his name and shouting “Boris out.”
The rapturous crowd, who had been standing in the cold for more than an hour in the hope of catching a glimpse of the Labour leader, hushed to near silence as Mr Corbyn spoke with neither notes nor a microphone.
Waving his newly published manifesto, he said: “Thankyou Sheffield for being here tonight. Thankyou for the lovely city you are.
“And thank you for your support for what we're doing to build a decent, fair society in Britain that cares for all, not just the few.”
Supporters started to appear on the concourse outside Sheffield Students' Union more than two hours before the programme kicked off - undeterred by a constant drip of rain and chilly temperatures.
As well as hundreds on the University concourse, more supporters lined the overpass stretching over the campus.
Mr Corbyn added: "Above all, it's about what we do in the next three weeks to convince people that what we're putting forward is a radical manifesto, it is different and it will change society."
A supporter on the overpass shouted: "Yes Jeremy. We'll keep the red flag flying."
Mr Corbyn went on: "And I want to do that because I'm fed up with the poverty, the homelessness, the food banks and the misery in so many people's lives."
He said he wanted to ensure Britain's trade in the future is secure "in or out."
Wrapping up his short speech, he said: "If Boris Johnson wants to go to Washington and do a deal with Donald Trump , I simply say this: Our NHS is not for sale."
He waved to supporters and headed into the Octagon Centre to prepare for the debate, as the crowd chanted "not for sale" back at him.
Asked how he felt after the speech, he told the Mirror: “Fine. Lovely people.”
Over the two hours, each leader will each be invited to take questions from the audience for thirty minutes.
The BBC's standard Question Time host Fiona Bruce will be hosting - and pushing the politicians to answer the questions.
On the show Fiona Bruce said: “Question Time has a proud history of giving the public - the voters - the chance to put their points and questions directly to their elected representatives. That’s never more important than during an election campaign.
"I’m very much looking forward to these special programmes."
