Dr Philip Nitschke plans to hold workshops across the UK
An Australian doctor stopped at Heathrow Airport when he arrived to hold workshops on euthanasia has been granted leave to stay in UK.
Philip Nitschke was interviewed under the Immigration and Asylum Act after arriving from Australia on Saturday.
Dr Nitschke plans to hold a workshop in Bournemouth, Dorset, on Tuesday to talk about assisted suicide.
The Home Office confirmed he had been interviewed and was later granted permission to enter the UK.
At no point was Dr Nitschke arrested.
Dr Nitschke said he had been surprised to have been detained and questioned, as he had been allowed into the UK to hold lectures before.
Dr Nitschke, who runs Exit International, told the BBC he had been searched, fingerprinted and formally interviewed after being told his workshops could be in breach of British law.
He said this had never happened to him before.
"I mean, this is a very fundamental question of free speech - people want to know about this," Dr Nitschke said.
"This is an important cutting-edge social issue and to find people thinking about deportation because the message is supposedly so worrying says something about changes in British society which are quite troubling."
Alex Russell, the vicar of Pennington and chaplain of Oak Haven Hospice in Lymington, Hampshire, said: "I'm not happy about the views that he expresses or these so-called suicide workshops.
"But I would always defend someone's right to voice an opinion about something and to say controversial things.
"The difficulty may be if people who are psychologically unable to think as clearly as they might, or people who are still quite young and forming their opinions, might be influenced by him inappropriately."
"As a hospice chaplain I have had contact with several patients who because of long-term chronic conditions have attempted to take their own lives.
"In every case they have said afterwards that they are glad to be alive and they're glad it didn't work."
After speaking at the Hamilton Hall Hotel in Bournemouth, Dr Nitschke plans to hold workshops in Brighton, Stroud, Gloucestershire and Glasgow.
Dr Nitschke, from Darwin, administered lethal injections to end four patients' lives after voluntary euthanasia was made legal in Australia's Northern Territory in 1996.
The Australian federal government overturned the law nine months later.
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