Home Office research into euthanasia revealed for the first time has found 30 per cent of "mercy killers" go on to commit suicide.

A report published by the Voluntary Euthanasia Society reviewed research over the past 10 years by the department about assisted suicide.

The group, which is campaigning for a change in the laws to legalise assisted suicide, claimed not enough evidence had been gathered by officials, while what was available showed that Britain's current laws were failing.

Part of its conclusions were based on Commons questions asked by Liberal Democrat MP Mike Hancock who had quizzed ministers over government research conducted into the issue during the last five years.

Britain currently has the toughest euthanasia laws in Europe and the issue has been raised by recent court cases including that of Diane Pretty, who lost a High Court challenge to request the right to die.

The society claimed people who help with euthanasia face a "legal lottery" which adds to the emotional burden and are unable to ask for support because of the risk that they may face criminal charges.

This is one of reasons the VES believes 30 per cent commit suicide themselves.

"This is a shocking statistic which highlights the range of problems under current law and should instigate further government research,'' said spokeswoman Tamora Langley.

"The government listed 15 pieces of research it had funded into suicide, but pointed out that none looked at suicide among the terminally ill, and that there had been no government-funded research into assisted suicide or voluntary euthanasia,'' she said.

Two other surveys this year showed around half of GPs have been asked by a terminally patient for help to die.

Officials at the Home Office sought to play down the claims by the VES, explaining that the issue is an emotive subject with considerable legal complications."Our law needs to take into account the value of life and the vulnerability of individuals who are ill and in pain," said a spokesman.

"That is why the law protects them. We have no plans to change the law at present."