A defiant Ken Livingstone insisted he had nothing to apologise for as he arrived at a misconduct panel facing fresh criticism from campaigners over his controversial comments about Adolf Hitler.

The former London mayor repeated his claim that there was "collaboration" between the Nazi leader and the Zionist movement before the Second World War and denounced the hearing as "unfair".

Around one third of voters believe he should be expelled from the party, according to polling, and the Holocaust Educational Trust said Mr Livingstone had persisted in causing offence.

The Labour veteran was suspended in April last year after claiming that Hitler supported Zionism in the 1930s before he ''went mad and ended up killing six million Jews''.

A hearing run by Labour's national constitutional committee that could last up to two days will decide if he should be kicked out.

But Mr Livingstone said the process was "completely unfair" and criticised the decision to hold it in private.

"They have dropped all the charges that I'm anti-Semitic," he told reporters. "They've dropped the charge that I said Hitler was a Zionist."

Mr Livingstone insisted he had nothing to apologise for, repeating his previous argument that he had only stated historical fact.

"I simply said, back in 1933 Hitler's government signed a deal with the Zionist movement, which would mean that Germany's Jewish community were moved to what is now Israel."

He added: "You had, right up until the start of the Second World War, real collaboration."

In a written submission to the panel released earlier this week, Mr Livingstone said he had ''raised the issue of the collaboration between Hitler and a section of Zionism in the early 1930s'' as a result of a misunderstanding of presenter Vanessa Feltz's question during a BBC London interview.

He said he had ''no intention'' to cause offence but was ''sorry'' if his remarks did so.

The ally of Labour leader Jeremy Corbyn said he had taken to the airwaves to defend the reputation of the party after MP Naz Shah had come under fire for social media posts she subsequently apologised for, and admitted contained anti-Semitic language, although Mr Livingstone said they were ''not obviously anti-Semitic''.

He faces a charge of engaging in conduct that was grossly detrimental to the party.

A ComRes poll for Jewish News found that 29% of voters believe Mr Livingstone should be expelled from the party over the comments, compared with 20% who did not.

The study also found that 34% of voters said allegations of anti-Semitism in the party made them "think twice about voting Labour" while 29% said they did not.

It is not the first time Mr Livingstone has become embroiled in an anti-Semitism row.

In 2006 a High Court judge said he made ''unnecessarily offensive'' and ''indefensible'' remarks likening a Jewish reporter to a Nazi concentration camp guard. But he was cleared of bringing the office of mayor into disrepute.

Karen Pollock, chief executive of the Holocaust Educational Trust, said Mr Livingstone had persisted in causing offence.

She said: "Even when it has been made blatantly clear that his comments have caused deep hurt and offence to Jewish people, and in particular to Holocaust survivors, still Ken Livingstone has persisted down this route - repeatedly invoking the Holocaust, promoting a misleading and misinformed version of history to further his agenda. Enough is enough."

Mr Livingstone, who is being represented by high profile lawyer Michael Mansfield QC, was previously expelled from the party when he announced he would stand as an independent in the London mayoral race after losing the Labour selection process.

:: ComRes interviewed 2,034 British adults online between March 24-26. Data was weighted to be demographically representative.