London Mayor Sadiq Khan has said he is deeply distressed by the Labour split, but admitted the party has been "shockingly poor" at dealing with anti-Semitism.
Seven MPs resigned from the Labour Party on Monday morning, amid tensions over Brexit and allegations of anti-Semitism.
They include former shadow cabinet ministers Chuka Umunna (Streatham MP) and Chris Leslie, alongside Luciana Berger, Gavin Shuker, Ann Coffey, Mike Gapes, and Angela Smith.
Mr Khan blamed the Conservative Party for "the chaotic Brexit process", but said Labour has not acted quickly enough to tackle anti-Semitism.
But he said he believed the Labour divide will make it more difficult for the party to be elected to govern.