"I regard this as a battle for the future existence of the Labour party".
Christine Shawcroft, a member of Labour's national executive committee and an ally of Lansman, said the recorded comments were "a non-story", and were primarily "a concerted attempt to interfere in the internal election in Unite for general secretary".
It emerged, March 19, that Jon Lansman, the leader and founder of the grassroots organization Momentum has told his supporters that it is likely to win the backing of Unite - which has 1.3 million members - if its current leader Len McCluskey wins a further term in the upcoming union election, which will then enable it to take control of Labour, moving the party further to the left.
Mr Watson told BBC Radio 4's Today programme "enough is enough, this has got to stop".
"We've never seen the biggest [British] union organising a political faction within the Labour party with the tacit approval of the leadership".
Mr Watson said he wanted Mr Corbyn to "deal with" Mr Lansman.
Jon Lansman was said to have told supporters he expected the union, together with the Communication Workers Union (CWU), to affiliate to Momentum if Len McCluskey wins his battle for re-election as Unite general secretary.
At the meeting, Lansman says that while he hopes Corbyn remains as leader, Momentum should seek to boost the left's representation in key Labour positions to secure rule changes that would help install a leftwing successor when he leaves.
Currently, a candidate must obtain the support of 15% of Labour MPs and MEPs in order to stand - a threshold a new left-wing contender is unlikely to be able to achieve.
Momentum launched a formal bid to affiliate with the Labour party in January, and warned its members that they will be expelled unless they join the Labour party by July. We will deny a voice to no-one.
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It seems the message did not get through, though, as they found themselves 2-0 down after just seven minutes. We knew we were coming on the back of an terrible away record and we wanted to try and put that right.
McCluskey had to show leadership over the issue, Watson said: "We could do with him trying to understand how important this is". In contrast, she suggested Mr Corbyn was a "moderate" socialist whose policies were "common sense".
Responding to initial attacks from Mr Watson, Mr Lansman said: "For 20 years the left was denied a voice".
"Our sole focus has to be a general election".
He also discusses an affiliation with the Unite union, the largest trade union in the United Kingdom and Ireland. They are welcome to do so.
"This is about democratising the Labour Party, which will strengthen the Labour Party".
"We can not have powerful people like Lansman saying secret plans to control the Labour party may be disrupted by a general election".
A Unite spokesman said: "As Unite has stated, repeatedly, it is for the Unite executive council, not the general secretary, to agree to which bodies our union aligns".
"It is extraordinary that the deputy leader of the Labour Party should interfere in Unite's democracy this way and it is very disappointing he was allowed to make his unsupported claims without being challenged, and that the BBC ignored the Unite statement which it had been provided well in advance", she said.