More than 150 Labour MPs and Lords have attended a meeting of a new group, in a bid to offset the influence of the party’s dominant left wing.

The event organised by deputy leader Tom Watson was attended by 14 members of Jeremy Corbyn’s shadow ministerial team.

Addressing the new social democratic Future Britain group, Mr Watson argued that the party faces its biggest ever schism unless it “restores pluralism and tolerance”.

The gathering saw followers of Tony Blair and Gordon Brown mix, having once engaged in bitter infighting, with Peter Mandelson telling the group they must “work together to save the party”.

Mr Watson announced that he would set up the group after 11 MPs quit the party, mainly over Brexit and antisemitism, with eight going on to form the new Independent Group with defecting Tories.

The Labour deputy leader said: “The last few weeks have been very difficult and upsetting. The departure of good people, in particular friends like Luciana [Berger] and Ian Austin, was for me a personal wake-up call to step up and do more.

“I really fear that unless we restore pluralism and tolerance to this party, it will be irreparably damaged and we will see a schism bigger than any we have experienced in our long history.

“This party is made of many elements and we’ve only ever worked and been elected to government when the pluralism of our different traditions has been respected.”

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Those at the event included leading Blairites such as Lord Mandelson, David Blunkett and Pat McFadden, as well as Brownites Stewart Wood, Yvette Cooper and Mr Watson himself.

Other senior figures in attendance were former leader Neil Kinnock and former deputy prime minister John Prescott.

In all, 13 former cabinet members attended the meeting, as did 14 current frontbenchers, including shadow transport secretary Andy McDonald, Gloria de Piero, Jim McMahon, Justin Madders and whips Mark Tami and Vicky Foxcroft.

Referring to Labour leader Mr Corbyn, Mr Watson said: “Jeremy to his credit kept the voice of his tradition alive through the campaign group during the New Labour years.

“So, he understands the need for those from the social democratic and democratic socialist traditions to give ourselves the strongest voice we can.”

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Among the policy areas the new group will focus on are foreign policy and defence, the future of work and pay, education and social mobility, and the future of the NHS and social care.

Darren Jones MP insisted the group was not a faction or a Labour equivalent of the Tory European Research Group (ERG).

Mr Jones told reporters: “Some have said that this is a new faction it is in fact the complete opposite.

“As Neil Kinnock, our former leader was saying this evening, and Peter Mandelson, this is a coming together of previous factions into the mainstream Labour Party.