Unite's acting general secretary Gail Cartmail insisted there were "no plans" to affiliate to Momentum and said Mr Watson's attack was "extraordinary". Lansman, a former aide to Tony Benn and Michael Meacher, had told a group of Momentum activists that he wanted super-union Unite to affiliate to Labour.
Dismissing the affiliation claims as "entirely inaccurate", Britain's biggest union also accused Tom Watson of a "misguided" campaign to interfere in Unite's internal democracy and its ongoing general secretary election.
"This is about democratising the Labour Party, which will strengthen the Labour Party".
Tom Watson vowed to confront Jeremy Corbyn and ask him to distance himself from claims his grassroots campaign group Momentum is planning to get financial backing from the union Unite. "This is high stakes, and I hope my fellow members are going to understand that - and our leader". For the record, Len McCluskey has never met Jon Lansman to discuss this or any other matter.
In the recording, Mr Lansman says the left needs to organise better to ensure it can influence candidate selections and get a candidate on the ballot paper if Labour's leader Jeremy Corbyn leaves the job - a position Labour's deputy leader Tom Watson said amounted to "entryism".
Talking about speculation that Theresa May could hold an early election, he said: "So we may well face an election this year and that will disrupt some of our plans, but we've still got to plan what we need to do next".
In the leaked recording, Mr Lansman issues a call to arms to Momentum supporters saying they need to make sure the Left is represented in key positions at all levels in the party. "We could do with him trying to understand how important this is".
John McDonnell today told the "i" newspaper it could take two years for Labour to be ready to fight a general election.
However, speaking on BBC Radio 4's Today programme, Watson said the plot could destroy the Labour party. "I'm afraid there are some people who do not have our electoral interests at heart", he said.
Mr McDonnell said: "What he is trying to do is influence the election of the general secretary of Unite and he has dragged the Labour Party into this, completely unnecessarily".
Through the deal, Momentum, founded four weeks after Corbyn's successful campaign for the Labour Party leadership, would hope to secure the long-term direction of the party.
"Many of our young members who have joined Momentum do not want to be involved in covert plans to take over the Labour Party".
She indicated that Watson and his allies were a bigger problem for the party. And I think this whole non-story - Jon said nothing that was at all controversial. But he clearly wishes to go back to the days of command and control on a Blairite model.
"We will deny a voice to no one", he said.
"It is not a question of anyone disaffiliating from the Labour Party and affiliating to Momentum instead".
There has been deep unrest within Labour following the 2015 election, which Labour lost, paving the way for a leadership contest which was originally expected to be won by a center-left frontrunner.
Jeremy Corbyn's deputy has claimed the party's future has been put at risk by the prospect of a hard Left takeover.