Asked about the apparent Conservative's double-digit poll lead, Corbyn yesterday said the election was not a "foregone conclusion" and told reporters to remember his unexpected Labour leadership victory.
Labour leader Jeremy Corbyn has failed to rule out including an offer for a second Brexit referendum at his first campaign event ahead of the General Election.
Supporting Corbyn's statement, Scottish Labour leader Kezia Dugdale, said: "I told the NEC there is already is a progressive alliance in the United Kingdom: it's called the Labour Party".
He said: "We don't accept that it is natural for Britain to be governed by a ruling elite the City and the tax-dodgers and we don't accept that the British people just have to take what they're given".
Mr Corbyn's speech came amid speculation about Labour's taxation plans, after Mr McDonnell suggested the wealthy, who he defined as earning over £70,000 a year, should "pay their way more".
TRT World's Sara Firth investigates the current state of the Labour Party. "The British people know that they are the true wealth creators, held back by a system rigged for the wealth extractors".
In Edinburgh, the First Minister of Scotland and leader of the Scottish Nationalist Party (SNP) Nicola Sturgeon said the SNP is the only party standing in the way of a Conservative majority "because it is "pie in the sky" to think Labour can win alone".
He added: "We can't win, they say, because we don't play their game". We can't win, they say, because we don't play their game.
"Labour will stand up for all children by building a schools system for everyone, keeping class sizes down and making sure schools and teachers have the resources they need to ensure that every child, whatever their background, has access to a world-class education".
But he will insist: "Things can and they will change".
May has called the election to increase the narrow 17-seat working majority in parliament she inherited from her predecessor David Cameron, who quit a year ago after Britons rejected his call to stay in the EU.
"There are many great Labour candidates and MPs and I will be fully supportive of them".
However, the last American and British elections, as well as the European Union referendum, have also showed that polls can be mistaken.
A YouGov opinion poll carried out after the election was called showed May's Conservatives on 48 per cent, with Labour trailing a distant second on 24 per cent.
Cameron won his majority in the 650-seat House of Commons in 2015 in part by taking seats like Lewes from the Lib Dems, who were punished by voters for going into coalition with Cameron's Conservatives five years earlier.
"We're putting a message out there: this country does not have to be so divided, there does not have to be such appalling levels of poverty and unachieved ambition because of people growing up in poverty".