People should be able to say if they wish to die, Baroness Warnock says
People with dementia should be able to end their lives if they feel they are a burden to others or to the NHS, according to a respected ethicist.
Baroness Mary Warnock, who has made similar calls in recent years, first made her remarks in a Church of Scotland magazine.
She told the BBC she believed there were many who "sank into dementia when they would very much prefer to die".
But Alzheimer's charities called her remarks "insensitive and ignorant".
Around 700,000 people in the UK have dementia and the number is expected to double within 30 years.
Lady Warnock says there should be more research to establish when people with dementia and Alzheimer's disease can still be regarded as mentally competent, so that they can make a decision that they wish to be helped to die if they reach a certain point in their illness.
"We need more research to find out at what point one can say people diagnosed with Alzheimer's or dementia are still mentally competent to make the decision that they would prefer to die, rather than be a burden on their families or the NHS."
She praised the recently introduced Mental Capacity Act which gives people the right to appoint someone to act for them if cannot make decisions themselves.
But she added: "I still think that there is a very huge number of people who sink into dementia and mental incapacity who would really very much prefer to die rather than continue in the state they are in.
"I think that's something most of us dread more then we dread any other form of dying."
Baroness Warnock said many people with dementia became unable to swallow - "that's one of the most horrible conditions to be in".
"If one wants to avoid that, one should have the entitlement to make it clear what one wants to do, before that situation is reached."
But Rebecca Wood, chief executive of the Alzheimer's Research Trust, strongly criticised the peer's comments.
"Lady Warnock demonstrates a shocking ignorance when espousing her highly insensitive view that people with dementia are 'wasting people's lives' and may have a 'duty to die.
"People with dementia can live quite comfortably when cared for properly.
"The solution to our dementia crisis is not euthanasia; the answer is more research so we can find new treatments, preventions and a cure.