Why is the mental capacity bill needed?
It gives legal backing to advance directives, or "living wills" under which patients can demand the right to die by refusing treatment when facing a terminal decline.

Any concern by a doctor over the validity of a particular living will would be judged in court, with doubts resolved in favour of preserving life.

The bill also gives patients the power to appoint a friend or relative to tell doctors to withdraw treatment if they themself are no longer capable of doing so, and to make decisions on finance. Those with no friend or relative to speak for them can have an independent consultee.

Who supports the bill?
The government, and charities such as the Alzheimer's Society, Age Concern and Mencap. They stress that living wills are used in common law but this legislation gives them statutory force.

Why is the bill opposed?
MPs are concerned that the bill introduces "euthanasia by the back door", and also could enable unscrupulous friends or relatives to order an incapacitated patient's death.

Critics also argue that people do not recognise that the legal definition of treatment includes food and water: by saying they do not want medical treatment, they could be dehydrated or starved to death. Another argument is that those who sign a living will often change their mind if they become incapacitated - and have no means of conveying this. And MPs also criticised the fact that, as the bill initially stood, living wills need not be written down or witnessed but could be based on conversations.

Any concessions offered?
Two: Living wills would have to be written and witnessed to constitute law; and where withdrawing "life-sustaining treatment" is concerned, the decision-maker must not be motivated by a desire to bring about death, irrespective of whether that is in the person's best interests.

What happens next?
The bill goes to the Lords for second reading on January 10 for the concessions to go before peers. The Department of Constitutional Affairs expects it to be on the statute book in the spring.

What can I put in a living will?
Patients cannot request the treatment they want (a decision for doctors), but only what they do not want.

You could request no antibiotics or resuscitation, but could not say you still wanted food and hydration, particularly since in some cases of terminal cancer, this can feed tumours. Doctors would have to look at any positive requests, but would in no way be bound by hem.