Former Labour leader Jeremy Corbyn has publicly criticised Keir Starmer for the first time, less than an hour after his successor declared the party was "under new management".
Mr Corbyn attacked Labour's decision to settle in court over a Panorama investigation into antisemitism when he was leader.
The move was "dissappointing" and a political decision not a legal one, he said.
Tensions between Labour's old and new leadership boiled over soon after Sir Keir appeared to try to draw a line under the past, telling MPs the party was “under new management”.
During his time as leader Mr Corbyn was accused of failing to adequately confront Labour's antisemitism crisis.
The issue hit the headlines last summer when a number of whistleblowers who worked for the party detailed what they had seen in a Panorama documentary.
Labour has now agreed to pay "substantial damages'' to seven whistleblowers over "defamatory and false allegations'' made following the programme.
The party also issued an unreserved apology to the former staff members and to John Ware, the journalist who presented the programme.
In a statement, Mr Corbyn said the decision to apologise and make substantial payments to former staff who sued the party in relation to the Panorama programme "is a political decision, not a legal one".
He also called for a leaked internal Labour report, which he said revealed evidence of “factionalism and obstruction of Labour’s 2017 General Election campaign”, to be considered by an ongoing Labour probe.
Len McCluskey, the boss of the Unite union and a staunch Corbyn ally, has also criticised the decision to settle the case.
A spokesman for Sir Keir pointed out that during the party's leadership contest earlier this year all three candidates pledged that they would seek to settle.
In a statement Labour said that before the Panorama programme was broadcast the party had issued a press release that contained “defamatory and false” allegations about their own employees and Mr Ware.
On the whistleblowers it added: “We unreservedly withdraw all allegations of bad faith, malice and lying. We would like to apologise unreservedly for the distress, embarrassment and hurt caused by their publication."
The damages are expected to be in six figures.
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