The former Archbishop of Canterbury Lord Carey has declared his support for new legislation to legalise assisted suicide, in direct opposition to official Church of England policy.

The announcement comes as the House of Lords next week prepares to vote on a bill proposed by Labour peer Lord Falconer, which would allow assisted suicide in cases where someone was mentally capable, and had six months or fewer left to live.

Lord Carey said "Today we face a central paradox. In strictly observing the sanctity of life, the Church could now actually be promoting anguish and pain, the very opposite of a Christian message of hope."

Recently locked-in syndrome sufferer Tony Nicklinson died after being refused the right to die, and Lord Welby said that the case had had the "deepest influence" on his change of heart.

"Here was a dignified man making a simple appeal for mercy, begging that the law allow him to die in peace, supported by his family," he wrote in the Daily Mail.

"His distress made me question my motives in previous debates. Had I been putting doctrine before compassion, dogma before human dignity?

"It would be very naive to think that many of the elderly people who are abused and neglected each year, as well as many severely disabled individuals, would not be put under pressure to end their lives if assisted suicide were permitted by law," he wrote.

Lord Carey had previously helped to block Lord Joffe's Assisting Dying for the Terminally Ill Bill in in the House of Lords in 2006, while still Archbishop of Canterbury.

Nicklinson's widow Jane welcomed Lord Carey's announcement.

"I'm amazed actually and thrilled because the Church has always been one of our greatest opponents," she told BBC Radio 5 Live.

"Someone shouldn't be forced to stay alive with daily suffering - his life was a living hell."

Current Archbishop of Caterbury Justin Welby continues to oppose assisted suicide.

Writing in the Times, he warned vulnerable people could be put at risk by the legislation.

"It would be very naive to think that many of the elderly people who are abused and neglected each year, as well as many severely disabled individuals, would not be put under pressure to end their lives if assisted suicide were permitted by law," he wrote.

Under the 1961 Suicide Act, someone found guilty of helping a person to commit suicide could face up to 14 years in jail.

Under the new law, two doctors would have to verify independently that the person was terminally ill and had reached the decision to die independently.