A Kirklees MP has apologised after an aide claimed she had “knifed” Labour leader Jeremy Corbyn.
Batley and Spen MP Jo Cox has become embroiled in the bitter row over the future of the party.
Mrs Cox, a first time MP elected last year, co-wrote a column in the Guardian last week expressing regret for nominating the controversial left winger and criticising his leadership.
This morning, Labour party members in her constituency received a newsletter email entitled “Why I Knifed Corbyn”.
Many thought the headline was inappropriate with one questioning the MP on Twitter why she had said that.
Mrs Cox replied that it was a mistake by a staff member.
Party members then received an email saying campaign manager, Dan Howard, had written the headline and had offered his resignation.
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In an apology sent to members, Mr Howard, said he was “mortified” by his mistake which had “offended many members and caused Jo an enormous amount of abuse”.
He said: “My headline was a sarcastic take on the media furore surrounding Jo’s comments in the media about the performance of our party and was completely inappropriate.
“Jo has not been disloyal to the party nor has she been disloyal to our leader.”
But in her Guardian column, published the day after local election results, Mrs Cox laid into Mr Corbyn’s leadership.
She said: “Weak leadership, poor judgment and a mistaken sense of priorities have created distraction after distraction and stopped us getting our message across.”
She added: “These elections were a terrible missed opportunity. We cannot afford any more.”
The Examiner contacted the office of Jo Cox but no one was available to comment at this time.