Boris Johnson’s appointment as Prime Minister has sparked growing concern that scores of Labour MPs are ready to step back from the fight against antisemitism under Jeremy Corbyn.

In a message that provoked widespread anger among Jewish Labour campaigners, Lucy Powell, Labour MP for Manchester Central, who has previously been vocal on the issue of anti-Jewish racism in her party, last week attacked what she called a “deeply unhelpful and divisive move” by Labour peers who were considering holding a vote of no confidence in Mr Corbyn over his failure to deal with the crisis.

Directing her words at Labour MPs and party supporters, Ms Powell said on social media: “All our attention should be facing outwards at a new Tory PM.”

Although Ms Powell is one of the few to be so explicit about the need to rally behind Mr Corbyn rather than pressurise him over antisemitism, the JC has spoken to a number of Labour sources who believe that Ms Powell’s tweet heralds a shift in the position of mainstream MPs who have claimed to be allies in the fight against antisemitism.

Mr Corbyn’s closest aides are understood to be convinced that a sizeable number of Labour MPs will now follow the lead of Ms Powell and prioritise the fight against Mr Johnson’s government over the fight against antisemitism.

Mr Johnson will be portrayed as an increasingly hard-right and divisive leader by the Labour leadership.

Labour also plans to circulate a message to all MPs that with under 100 days before the October 31 “do or die” Brexit deadline imposed by Mr Johnson, they should concentrate entirely on attacking the new Tory leader.

One MP told the JC: “Corbyn’s lot know that Lucy Powell is not the only one among the PLP (Parliamentary Labour Party) that can be convinced to put the antisemitism concerns on the back-burner. There’re other Labour MPs, most of whom are facing the threat of reselection from members in their own local constituencies, that can be made to toe the line.

“It’s hard to justify carrying on screaming about the party not doing enough about antisemitism at the same time as someone who is committed to taking us out of Europe without a deal and has been linked with hard-right of the Tory Party has just come to power.”

In recent weeks hard-left Momentum activists have targeted Labour MPs deemed to have failed to support Mr Corbyn strongly enough with the threat of being deselected under a new “trigger ballot” system which can be started if one third of local party members raise concerns about their MP.

But other Labour MPs have told the JC that they are furious at suggestions they should automatically step in line with the leadership because of Mr Johnson’s rise to power.

“Jeremy Corbyn and Boris Johnson are different sides of the same coin,” one parliamentarian said.

“Jeremy Corbyn is the reason Labour is tanking in the polls. If Jeremy Corbyn’s outriders think he walks into Number 10 just because he isn’t Boris Johnson they’ve got another think coming.

"Jo Swinson, Nicola Sturgeon and Caroline Lucas are coming for Labour voters and it’s only the hubris of self-serving Corbynistas that will keep Johnson in power.”

Another Labour MP, whose constituency is in the north of England, added: “The antisemitism problem is the Labour Party’s own, unique problem. We are not fit for government unless we sort it out.”

“We should never have been in the position where we have a Tory government led by Boris Johnson,” said another MP. “Labour should have returned to power long before this. I do think the PLP recognise that antisemitism is pulling the party down.”

On Monday, at an extraordinary meeting of Labour peers, it was decided not to press for a vote of no confidence in Mr Corbyn but to leave the issue hanging until September, at which point the leader’s response to the antisemitism crisis would be reviewed.

The peers also called for shadow Brexit minister Baroness Hayter to be reappointed to her post after she was sacked for comparing Mr Corbyn and his team to Adolf Hitler’s final days in the bunker.

A source said: “There were around 80 peers in the room. No-one spoken up in favour of Corbyn. ‘We can’t fight Boris Johnson unless we get our own house in order’ was very much the message of the meeting.”

As Mr Johnson took office on Wednesday, CFI chairmen Stephen Crabb MP and Lord Pickles, and Honorary President Lord Polak said in a statement: “From his refusal to boycott Israeli goods in his time as Mayor of London through to his instrumental role as Foreign Secretary in both the landmark Balfour Declaration celebrations and the first-ever official Royal visit to Israel, Boris has a long history of standing shoulder to shoulder with Israel and the Jewish community.

“Mr Johnson continued to display his resolute support throughout the leadership contest with a memorable hustings event with CFI and an excellent letter penned to CFI’s supporters reiterating his deep support for Israel and pledging to be a champion for Jews in Britain and around the world’.”

The Board of Deputies also issued a statement wishing Mr Johnson “every success as Prime Minster at this critical time for our country” and added they had enjoyed a “long and positive relationship” with him as both Mayor of London and Foreign Secretary.