The chairman of the Southbank Centre has been accused of comparing Reform voters to Nazi supporters.
Misan Harriman, who is friends with the Duke and Duchess of Sussex, also said the soaring popularity of Nigel Farage's party is 'a warning'.
In a clip posted on Instagram, he referred to a conversation between Holocaust survivor Susan Sontag and US author Kurt Vonnegut about the rise of the Nazis in 1930s Germany.
The late Ms Sontag said: '[Some] 10 per cent of any population is cruel, no matter what, and 10 per cent is merciful, no matter what, and the remaining 80 per cent can be moved in either direction.'
Mr Harriman said the comment was 'really topical' in light of the local election results.
He went on: 'The surge of Reform is real. It is a surge, and it should be a warning and a rallying call at the same time.
'We all have to have discussions, and with many people who voted for Reform. They're not devils, they've been just reading certain newspapers, listening to certain charlatans.'
He went on to mention newly elected Reform councillor Glenn Gibbins, who was suspended over the weekend for tweets from 2024 that said Nigerians in Sunderland should be 'melted down to fill in the potholes'.
The chairman of the Southbank Centre, Misan Harriman (pictured), has been accused of comparing Reform voters to Nazi supporters
Darren Grimes, the Reform deputy leader of Durham County Council, agreed there had been 'a failure of the vetting process'.
Some were quick to criticise Mr Harriman.
Fiona Sharpe, of Labour Against Antisemitism, said he should be 'removed from his prestigious role at the Southbank Centre', adding: 'Whatever his political views are, to diminish the systematic state sponsored murder of six million Jews, just for being Jews, in this particular climate in Britain, is abhorrent.'
Holocaust Educational Trust chief executive Karen Pollock said: 'This is shocking. Whatever one's political view, how on earth could yesterday's election results ever be comparable to the Holocaust – the mechanised state sponsored murder of six million Jews by Nazis and their collaborators?'
Reform's Treasury spokesman Robert Jenrick said: 'Comparing the millions who voted Reform on Thursday to the Nazis is disgusting. This crass moron should be nowhere near a taxpayer-funded organisation.'
However, others spoke up for Oscar-nominated filmmaker Mr Harriman.
Faiza Shaheen, executive director of Tax Justice UK, said: 'Absolute solidarity with the incredible Misan Harriman.'
Podcaster and former Sunday Telegraph deputy editor Matt d'Ancona said the idea that Mr Harriman should step down over his views was 'disgusting'.
Reform's Treasury spokesman Robert Jenrick (pictured) called Mr Harriman's comparison 'disgusting'
'The ability of people to be able to say what they think is more important than anything else,' he said.
Mr Harriman said his words had been taken out of context. 'I use a quote from a conversation with Kurt Vonnegut and Susan Sontag, in which she discusses human behaviour after studying the Holocaust,' he said.
'In that context, I talk about human behaviour and how we can build community in the lead-up to the next general election.'
The Southbank Centre is London's biggest arts venue, and home to the Royal Festival Hall, which recently received £10million from Arts Council England.
A spokesman said: 'The Southbank Centre condemns all forms of anti-Semitism, hatred and discrimination. The personal views of individual members of our board do not represent the views of the Southbank Centre.'