Former Cabinet minister Tessa Jowell has warned Jeremy Corbyn and his allies not to turn Labour into a “sect” which is “obsessed with rooting out heresy”.
In her maiden speech to the House of Lords, newly-ennobled Baroness Jowell said that the party had to use its expanded membership to unite, rather than descend into factional in-fighting.
The former Culture Secretary and Minister for the Olympics said that Labour could only help the poorest if it was in Government.
And she signalled that Corbyn supporters should not seek to drive from the party those who disagreed with them.
Despite repeated denials by Momentum supporters, Labour MPs worry that they face a round of deselections ahead of the 2020 general election, not least as many seats are up for boundary changes.
Flanked by Baroness Rebuck, the widow of New Labour guru Philip Gould, Baroness Jowell said: "What I wish for my country, I wish for my own beloved Labour Party.
“I hope it can embrace the energy of its new and growing membership who all share a belief that we should help people achieve more together than they can alone.
“My party can only do that when it governs. It fails when it becomes a sect of the Elect – turning its back on those who are not true believers, obsessed with rooting out heresy."
Some of the Parliamentary Labour Party (PLP) believe that Corbyn will stage a Shadow Cabinet reshuffle after the EU referendum, possibly taking 'revenge' on figures such as Hilary Benn, who supported the bombing of ISIL in Syria, and possibly the Whips' Office.
One 'heresy' that some Labour MPs believe is being targeted by Corbyn supporters is support for Tony Blair and the Iraq war.
With the Chilcot report due next month, it is expected that Corbyn will use its conclusions to renew previous calls to try the former Labour Prime Minister for 'war crimes'.
Baroness Jowell, who was defeated by Sadiq Khan for the Labour candidacy for Mayor of London last year, paid warm tribute to her former rival.
But she said recently of the Labour selection race for City Hall: "I didn't win because the Labour Party turned left".
Today, she stressed that she had a long record “in defending a just cause even when it is unfashionable”.
In a wide-ranging speech, she pointed to her record as an MP for more than 23 years, and how she first became politicised as a social worker in London.
"I hope I will never become inured to what poverty smells like," she said.
And the former minister warned the Tories not to try to neuter the House of Lords after a string of defeats over issues like tax credits, disability cuts and child refugees.
“Tax credits, support for disabled people, social housing: all these are causes that will change the lives of hundreds of thousands of people. All causes taken up by your Lordships.
"So I say to the Prime Minister in the light of proposals in the Loyal Address that however he may feel thwarted by this House, bad and unfair laws are not improved by curtailing the power of scrutiny in this place.”
Earlier in her speech, Baroness Jowell, who served under both Tony Blair and Gordon Brown, urged the country to unite in its support for the European Union.
“Amid the daily salvoes from warring economists and the claims and counterclaims of the partisans, it is too easy to forget that the EU is a union of 28 nations - in a continent which saw the deaths of 70m from wars in the last century - who have bound themselves together by common commitments to standards of human rights, democracy, the rule of law and peaceful co-existence. We should never take that for granted.”
The former Cabinet minister said that while she respected the views of those who wanted to vote ‘Leave’ in the referendum, she detected “a deep pessimism” among the Brexit camp.
“Of course I respect the sincerely held views of those who want to leave, but behind the ‘go it alone’ rhetoric, I detect a deep pessimism.
“Those who wish to make this leap in the dark discount our importance to the rest of the EU, and the fact that our active engagement in it is a force for stability and good sense, a matter of vital national interest. It’s a view which betrays a lack of confidence in their own country, and its capacity to lead.”
Baroness Jowell pointed out that the EU In campaign depended on cross-party alliances, just as the Olympics had.
Praising Tory peers Lord Coe and Lord Deighton, she said both Labour and Tory governments could be proud that they had made “a world class venue out of wasteland”.
“We did inspire our young people. We did lead the world in sport after sport. And in that summer we found a renewed sense of our national identity – a self-confident and diverse country – which took us all a little by surprise,” she said.
“In those summer weeks - to recall Abraham Lincoln - we found ‘the better angels of our nature’. And I hope that in that same spirit the people of this country will renew its commitment to the EU as an optimistic community of nations, in which proud national identities are also the foundation of collective solidarity and open trade.”