Watson also said that if members at Labour's annual conference in Liverpool backed the idea of holding a "people's vote" second referendum on Brexit, it would be hard for the party's leadership to ignore it.
Lewin added: "I wanted more for Remain Labour supporters and other grassroots campaigners, but we have a motion that effectively calls for Labour to support the EEA as a minimum, rejects the idea of a referendum exclusively on different forms of Brexit and increases the chances of a People's Vote".
The Labour leader said today that he would prefer forcing a general election this autumn instead of a second referendum but promised to "adhere to what members want".
To cheers he highlighted that people from across the United Kingdom were present, saying: "They are saying squarely to the leadership of the Labour Party "listen to us, hear us, give us a People's Vote".
"Our preference would be for a general election and we can then negotiate our future relationship with Europe but let's see what comes out of conference", he told the BBC's Andrew Marr Show, saying Labour was ready to vote against any deal.
And he indicated that even if the decision on the European Union was put to the public in a referendum, the choice would be between accepting a deal or returning to the negotiating table rather than the option of remaining inside the bloc.
Labour MP David Lammy said it would be "farcical" to offer a referendum between "no deal or a bad deal".
Corbyn wanted his conference to be an opportunity to sell his alternative vision for Britain's economy, pressing his argument for the renationalization of rail, mail and utilities, and to rally the party for a possible early election.
Labour leader Jeremy Corbyn has long opposed the idea of such a vote.
The Labour Party features on numerous front pages on Monday as politics dominates the headlines.
Reforms to Labour leadership elections and the selection process for would-be MPs have been supported by delegates despite splits between constituency parties and unions. Current rules say a majority of local members must demand a new contest.
Mr Watson told The Observer: "Jeremy and I were elected in 2015 to give the Labour Party back to its members".
"My big worry is that if we go for a referendum which is seen as just a simple re-run we could divide the country again, we could get nearly the same result or if it's slightly different that people demand another referendum".
"And if there is a general election and we are in office we would go straight to the negotiating table".
But, he added, he would advise Mr Umunna, to "get behind the leadership" and the party's policies "and help us work towards a Labour government".