A former GP dubbed Doctor Death dared police to prosecute him today as he was questioned by officers for helping a terminally ill man pay for assisted suicide.
Dr Michael Irwin, 78, vowed to highlight the "hypocritical British system" surrounding euthanasia as he was eventually taken to a station in south London.
Dr Irwin had expected to be taken to Shoreditch station in north London but, after media gathered in Hackney for his arrival, he was diverted elsewhere.
A Scotland Yard spokewoman said: "A 78-year-old man was arrested this morning and taken to a south London station."
Dr Irwin was being quizzed after writing a cheque for £1,500 towards the cost of 58-year-old Raymond Cutkelvin's procedure at Dignitas.
Before arriving at the police station, he said: "I am daring them to prosecute me. It is a hypocritical British system that allows the rich to seek treatment but the poor to face prosecution."
Mr Cutkelvin, of Hackney, east London, was diagnosed with an inoperable tumour of the pancreas in 2006 and died the following year at the clinic.
Dr Irwin was supported today by Mr Cutkelvin's partner of 28 years, Alan Cutkelvin Rees, 57.
Mr Cutkelvin Rees said: "I will do all I can to expose this absurd law.
"I have no trouble with the police, it's the system which has stopped me from grieving."
Dr Irwin insisted he would welcome a criminal trial, claiming he would be "open" with police about the role he played in Mr Cutkelvin's death.
"The two individuals, Raymond who was dying and his partner Alan, were not very well off financially and I was willing to pay one-third of the total cost involved in making that journey.
"I think it is the height of hypocrisy in this country where if you have the money, you are terminally ill and you want to go to Switzerland, you can do so."
Dr Irwin congratulated Debbie Purdy's triumph at the High Court in seeking to clarify the law on assisted suicide.
But he said: "It remains to be seen whether this will have positive wider implications."
The retired GP was struck off the medical register in 2005 by the General Medical Council (GMC) after he travelled to the Isle of Man with the intention of giving his friend, Patrick Kneen, about 60 Temazepam sleeping pills to help him die.
But Mr Kneen, who was in his late 70s and had prostate cancer, was too ill to take the class C drug and died a few days later while in a coma.
The GMC struck Dr Irwin off the medical register, saying his actions had been "unprofessional", "inappropriate" and "irresponsible".
Dr Irwin, of Cranleigh, Surrey, stood down as chairman of the then Voluntary Euthanasia Society, now renamed Dignity in Dying, after receiving a police caution over the incident.