An imam of an east London mosque has been subject to death threats and intimidation for expressing his views on evolution and women's right to refuse the veil.

Dr Usama Hasan, vice-chairman at Leyton mosque and a senior lecturer in engineering at Middlesex University, ceased delivering Friday prayers after 25 years of service when 50 Muslim protesters disrupted his lecture by handing out leaflets against him and shouting in the mosque for his execution.

A statement from the secretary of the mosque, Mohammad Sethi, that was leaked to extremist websites, said Hasan had been suspended after his lecture resulted in "considerable antagonism" from the community and for his "belief that Muslim women are allowed to uncover their hair in public".

Sethi's letter, dated 24 February, said Hasan's views were in "violation of the constitution of the Masjid Trust" and that the decision had been made for the "safety and security of all parties".

But Suhaib Hasan, who is the imam's father and chairman of the mosque, posted a counter-statement on the mosque's website on Thursday. It claimed his son had been the victim of a "vicious and predetermined agenda" by a "faction of trustees" and their decision to remove him was void because their meeting was inquorate.

The chairman said the threats and disruption had come largely from Muslims outside the mosque's community.

The death threats against Hasan were made in an anonymous leaflet handed out by protesters. It quotes religious authorities saying that any Muslim who believes in evolution is an "apostate" who "must be executed".

Hasan says he believes the leaflets were produced by the website Islamic Awakening. The website's leader, Abu Zubair, has led a long campaign against Hasan including making threats when Hasan was delivering a lecture in January.

An online petition against Hasan has apparently attracted 1,100 signatories, although they are not listed publicly. The petition says they are "horrified" by his views on evolution and call for him to be removed before the mosque becomes a "hotbed of modernist extremism".

Suhaib Hasan said the petition was set up in the name of the mosque illegitimately by trustee Arif Saleem, a man Usama brought on to the trust two years ago after they studied together at Imperial College.

Hasan, who has taken out extra security on his house where he lives with his wife and four children, said he was adamant he would not be leaving the mosque, although he would not be returning to give prayers for the time being.

"I'm not leaving," he said. "I've been here for 25 years and I fear that the mosque could fall into the hands of extremists. There are plenty of other mosques in the country that have gone that way. My supporters [at the mosque] don't want that and are encouraging me to stay to fight our corner.

"I've stopped giving prayers because they were interrupted by outsiders who were making some women members feel intimidated. Most people come to the mosque once a week for a quiet space to pray and find peace and inspiration and I want to respect that."

However, he did issue a statement apologising for some of his "inflammatory" statements about evolution and retracted them.

Maajid Nawaz, executive director of the Quilliam Foundation, a thinktank on Islamic extremism where Hasan has worked, expressed concern about the case.

"Dr Hasan comes from strong Islamist routes and is the son of a famous Wahhabi scholar," said Nawaz. "It's terrifying that he is being hounded out of his position. I question the support the police and government have given him, particularly after the prime minister's recent comments that we should be doing more to support Muslims who stand up to extremism.

"Until Cameron's speech, government policy has sent a message that it's OK to be an extremist as long as you don't blow yourselves up. But if extremists like these are left to be the gatekeepers of our communities, we're in real danger."

Hasan said the police had been slow to take the death threats against him seriously, but that they were now monitoring his case.

Harun Yahya, a popular Islamic creationist scholar from Turkey, begins a UK tour in London on Monday, adding to the debate. Last December Salir al-Sadlan, a senior Saudi-based scholar Salir al-Sadlan, said Muslims shouldn't pray behind someone who believed in evolution in a speech at Green Lanes mosque in Birmingham.

Inayat Bunglawala, chair of Muslims4UK, a group promoting Muslim engagement in British society, said there was "widespread ignorance" about evolution among the Muslim community. "Many traditional imams are grounded in ancient books in Arabic but have very little grounding in science. I find it staggering how they can be so strongly opposed to evolution without reading about it. That seems to be opposite of the very first commandment of the Qur'an, which is to read," Bunglawala said.

"Some of the language being used by Dr Hasan's opponents smacks of fanaticism. The shame is that, if his congregation do reject him, then it may well deter other imams from undertaking a study of evolution and speaking about what they have learnt."

Islamic Awakening and other members of the mosque could not be reached for comment. Hasan said the dispute over his suspension would be taken to the charity commission if it was not resolved soon.

"I've been a Londoner all my life and I grew up in that mosque," Hasan said. "I'm very passionate about living our lives in a modern way but, as far as they [my opponents] are concerned, that makes me an extremist. I'm going to have to live with extra cautions for the rest of my life."