A Palestinian human rights activist will not make a planned appearance at a Labour Party conference fringe event after his UK visa was delayed.

Omar Barghouti, co-founder of the Boycott, Divestment and Sanctions (BDS) movement for Palestinian rights, was due to speak at the event alongside the shadow home secretary, Diane Abbott, the Unite general secretary, Len McCluskey,and Labour MP Lisa Nandy.

Barghouti applied for his visa on 2 September, but was later told his application would not be processed within the normal timeframe.

In an email sent to Barghouti, the British embassy in Amman wrote: “Unfortunately, the processing of your application has not been straightforward and we have been unable to make a decision on your application within our customer service targets.” The application has still not been processed.

Barghouti was due to speak at The World Transformed, Momentum’s alternative Labour conference in an event titled “Palestine in the age of Trump”. He will appear through video link instead. He said he believed the delay to his visa was politically motivated.

“This is a desperate attempt to silence Palestinian human rights defenders, especially BDS advocates, who challenge not only Israel’s regime of settler-colonialism and apartheid but also UK complicity in maintaining this regime,” Barghouti said.

In April, Barghouti was barred from entering the US, where he was scheduled to meet with policymakers and journalists. He has previously visited both the UK and the US.

He added: “Israel’s escalating war on BDS, supported mostly by far-right regimes and autocratic populists, follows Israel’s failure to stop support for Palestinian rights and BDS from growing worldwide.”

The move to delay the visa was welcomed by the group Sussex Friends of Israel. A spokesperson for the group said: “Omar Barghouti is a man who, while campaigning for the end of a Jewish State, was happy to avail himself of the Israeli academic system and currently studies at Tel Aviv University. A man whose every statement is a violation of the IHRA definition of antisemitism. He is an extremist and should not be allowed to import his hateful views into our country.

“That the shadow home secretary feels it is appropriate to appear on the same platform as him, even through a video link, shames the Labour party.”

A spokesperson from The World Transformed said: “Omar Barghouti is an internationally renowned human rights defender working to amplify the voice of the Palestinian people struggling for their internationally recognised rights. We were excited to welcome him to The World Transformed festival to share his perspective and experience of the criminalisation of solidarity, a problem which this incident further highlights.”

Kamel Hawwash, chair of Palestine Solidarity Campaign, said: “This abnormal delay in processing Omar Barghouti’s visa application comes in the context of statements by UK government ministers expressing their intention to suppress UK support for the Palestinian-led BDS movement. Omar’s voice will be heard at the Labour conference and all of those committed to supporting universal principles of freedom, justice and equality will continue to stand strong in solidarity with the Palestinian people.”

A Home Office spokesperson said: “Our service standard is to decide straightforward applications within 15 working days, although more complex cases take longer.

“Mr Barghouti’s application remains within this target and he will receive a decision shortly.”