The British medical professor who was prevented from delivering a lecture on euthanasia in Cork on Holy Thursday has written to President Mary McAleese to complain about his treatment.

Prof Len Doyal, who holds posts in medical ethics in the universities of London and East Anglia, also claims gardaí did nothing to stop the protestors who violently forced the lecture at Cork University Hospital to be abandoned.

Doyal was invited to speak at the hospital's ethic forum's annual lecture, but before he could begin, an angry mob entered the auditorium. Writing to McAleese, Doyal outlined what happened.

"The Chair of the meeting and I were surrounded by an angry mob, who shouted, among other things, that I was a 'murderer', a 'Nazi' and had no respect for human life. One person next to me said that if I tried to speak, he would personally stop me and that I was not welcome there or anywhere else in Ireland.

"The police made no effort to remove this potentially violent mob; they were simply allowed to continue. It was left to three hospital security guards to escort me out of the hall, after I told the Chair that I could not speak in the face of such intimidation."

A garda spokesman said no complaint was made to local gardaí, either by Doyal or the hospital authorities. "The protest was a vocal one and not deemed to be a breach of the peace," he said.

In the letter, Doyal pointed out that he believed there should be a debate over "decisions about not providing life-saving treatment or about its withdrawal from severely brain damaged patients. I argue that while such practices are actually legal their current clinical justifications lack moral coherence. This results in vulnerable patients being put at risk of a lingering death and great suffering."

However, his motivation in writing to the president was the what he interpreted as an attack on free speech.

"It is the issue of free speech which is the basic motivation for my open letter to you. No one who has read my writings on the subject of euthanasia, or heard my lectures, could possibly regard them as advocating anything other than more understanding and compassion for suffering and terminally ill patients.

"The mob that refused to allow me to speak never heard any of this. I fear that this reflects badly on your country and on the officials that stood by... Last Thursday evening in Cork was not tragic for me but for Ireland."