"I just like him, you know what he does and all of that, helping the homeless, all of that, just interests me", he said.
Chancellor Philip Hammond said: "There is a £58 billion black hole in Jeremy Corbyn's manifesto - and it will be paid for by every single family in the country with higher taxes and more debt".
The party is being hosted by the Grand Marshal Corbyn's Patriotic Meme Collective, a pro-Labour campaign group.
The relentless rain didn't put a dampener on spirits and the mood of the crowd congregated on Manor House Grounds was one of unrestrained enthusiasm, there were intermittent chants of "Corbyn" and "Jeremy", flags being waved, one man was even banging a ginormous drum.
"I think therefore it's going to be interesting to see what happens over the next few weeks".More news: Venezuelan leader to President Trump: 'Get your pig hands out of here'
McCluskey's intervention came hours after Mr Corbyn launched his party's manifesto, which the Labour leader described as a "program of hope" "I believe that if Labour can hold on to 200 seats or so it will be a successful campaign", he said.
Yesterday, the Labour Party published its full manifesto for the upcoming General Election on June 8.
Questioned about policy issues, Mr Gething said Labour was "appalled" that the Conservatives were planning to abandon the "triple lock" guarantee on pensions, and claimed working people were worse off under the Tories.
"It matters whether I think this country will be better off having a Labour prime minister than a Tory".
Corbyn then spoke about Labour's plans for economic development, pledging investment into infrastructure, sustainable energy and industries.
Labour sems to have enjoyed a jump in support after its manifesto launch, gaining eight points in the latest Ipsos MORI/Evening Standard poll.
The Tories are now on 45 per cent, down four points since last week, while Labour was on 32, up one point - leaving Theresa May's party with a 13 point lead.