John McDonnell is “worried and saddened” by the prospect of a Labour split and has appealed to MPs considering leaving the party to engage in dialogue with the leadership.

In an exclusive interview with Jason Cowley in next week’s New Statesman, McDonnell’s first since the summer recess, the shadow chancellor admitted that he wanted to avoid a split "at all costs". Addressing the party’s anti-Semitism crisis, he repeatedly pledged to resolve the issue “as quickly as possible”.

On Tuesday, in an extraordinary intervention in the New Statesman, the former chief rabbi Jonathan Sacks denounced Jeremy Corbyn as an “an anti-Semite” and described the Labour leader's recently reported 2013 remarks on Zionists as “the most offensive statement made by a senior British politician since Enoch Powell’s 1968 ‘Rivers of Blood’ speech”.

Two days later, Frank Field, the veteran MP for Birkenhead, resigned from Labour’s parliamentary party in protest at what he called the leadership’s “tolerance” of prejudice against Jews. He described Sacks's remarks in the New Statesman as the “final straw”.

Labour MPs have been preoccupied by the prospect of split for much of the summer, with debate intensifying after a New Statesman cover story revealing the likelihood of a split by Stephen Bush last month.

McDonnell's attempts to defuse tensions within the party over anti-Semitism and avert a split are the most conciliatory comments by the Labour leadership yet and reflect its growing fears about the electoral damage a split could cause. The shadow chancellor told the New Statesman that it would be “disappointing” if Labour MPs were considering splitting for the sake of “individual personal careers” but struck a largely emollient tone.

In a direct appeal to colleagues considering quitting the party, he stressed that the leadership had an “open door”.

“Yes, I think there are people who are willing to leave the party,” he said. “I think I'm saddened by that. I really am saddened and I'm disappointed.”

Stressing that disagreements over anti-Semitism, Brexit and MPs' careers could be addressed internally, the shadow chancellor said he was worried that colleagues could leave. “If those are the issues that people want to split on, these are all issues which can be dealt with within the party.

“And I don't see them as fundamental issues that would encourage a split because there are opportunities for people not just to express their views but actually sometimes to win the argument as well.

“So I don't understand why there is this sort of pre-emptive move to split off. So I'm worried and I'm saddened by that and I think that open door is always there to prevent that happening because any split is automatically damaging.”

Asked whether he believed Labour would be better off without those MPs considering leaving, he urged them to stay and attempt to “win the argument” on policy issues. “ I don’t think any split is good,” he said. “My view is that this concept of the party as a broad church is a good thing.

“I’m a great admirer of Harold Wilson’s approach - it was robust, they had rows, but they came up with some good policies as a result. Sixties Wilson in particular, you’d have a situation then, where you want people challenging you, and if you do it within the right terms, that can be nothing but healthy.

“I lost a debate for 30 years, and I stayed within the party. there’s always that hope. I think the nature of Jeremy’s politics...it’s not to alienate people, it’s to bring people in.”

Invoking Labour’s loss to the Conservatives in his own Hayes and Harlington constituency in 1983, McDonnell warned would-be splitters that they risked a Tory victory if they left the party for a new entity.

He said: “If you’re having people like the SDP standing in particular constituencies, it takes votes away from Labour, And as a result of that where it could be very tight in individual constituencies we could be in a situation where Labour don't pick up those seats. And what does that mean? It means the Tories getting in.”

He added: “So the issue for me is I'd want to avoid at all costs a split if we can. That's why I'm saying I don't understand why people are more motivated in that way on any of these issues. There’s open democracy within the party. They may well win their arguments on some of these issues, and if it is about individual personal concerns just come and see us because there's a role for every order."

McDonnell acknowledged that Labour’s anti-Semitism crisis had led some MPs to consider their position and said: “Basically we've got to resolve it and we will resolve it and that's it.”

Though McDonnell stopped short of explicitly calling for Labour to adopt the International Holocaust Remembrance Alliance guidelines on anti-Semitism, he stressed the need for Labour to resolve the issue “as quickly as possible”.

He said: “I've been arguing that we need to resolve it in a way that brings everyone together and uphold all the views that have been expressed. The NEC now can close this one.

“My view is this. I want it resolved quickly. People have expressed their views on how to resolve it...I think we should listen to all these voices that are being heard, resolve the matter amicably and then move on as quickly as possible to tackling the real issues that are exciting for us.”

In his most candid public remarks about the crisis to date, McDonnell said he understood the strength of feeling within Labour over anti-Semitism and added that it had hit the party “to the core”.

“It’s really upset me,” he said. “I worked with Margaret [Hodge] for 30 years and we go back to London Labour. We fought together on racism and abolition.

“As I said before, it has hit us to the core ... I think we can come out of it as the anti-racist party that we are tackling the real issues. As I said before I don’t want to live in a society where synagogues are attacked, or where Jews graveyards daubed with swastikas or worse, Jewish children having to have security at their schools. It can't. That's unacceptable.”

McDonnell also revealed that he personally assured Hodge, the veteran Jewish MP who was threatened with disciplinary action by Labour after calling Corbyn an anti-Semite, that he would resolve the row.

He said: "When I listened to her interview on the Today programme, I realised she actually misunderstood my interpretation of the definition, examples and the code that was put forward and I thought but if she has misunderstood it in that way, others would have, I can understand why they feel so strongly.

“I gave her a ring soon after. And at that point in time I said look we need to resolve this as best I could and I'll do everything I can to resolve it. That's what I'm trying to do now. The key issue for me is resolve this now, so we can get out there as a real campaigning force on racism and anti-Semitism.

He nonetheless defended Corbyn’s role in handling the row and said the Labour leader was “listening to people now, and then coming to a consensus view”.

Jason Cowley’s full profile of McDonnell will appear online and in the New Statesman next week.