An 83-year-old woman has been arrested in connection with the death of a multiple sclerosis sufferer in Surrey.
Libby Wilson, a former GP and right-to-die campaigner, has been questioned on suspicion of aiding, abetting, counselling or procuring a suicide.
Surrey Police said the arrested woman attended Woking Police Station on Monday by appointment.
A spokesman for the force said the arrest was in connection with the death of Cari Loder, 48, of Farncombe.
Ms Loder, who had lived with the condition for many years, died at her home on 8 June after her condition deteriorated.
She reportedly spoke with Ms Wilson, a member of the Glasgow-based pro-euthanasia group Friends At The End, days before her death.
A man in his 70s from the Godalming area and a man in his 50s from west London have already been arrested on suspicion of helping Ms Loder to end her life. Both were bailed until 18 November.
New guidance was issued last week to clarify the law on assisted suicide in England and Wales.
Keir Starmer QC, Director of Public Prosecutions, spelled out the range of factors that would be taken into account when deciding on cases.
They included whether there was a financial motive, and looking into how the decision to die was made.
The guidance did not represent a change in the law, under which assisting suicide is illegal and carries a jail term of up to 14 years.