His change of heart follows Geoffrey Whaley, a terminally ill man, ending his life at Dignitas in Switzerland on Thursday

Vince Cable has called for assisted dying to be legalised, becoming the first party leader to back the move.

In a moving article that will reopen the debate around the emotive subject, the Liberal Democrat leader called for Parliament to introduce new laws.

His change of heart emerged as Geoffrey Whaley, a terminally ill man who ended his life at Dignitas in Switzerland on Thursday, said police inquiries about his wife’s role had marred his final weeks.

Writing for the Mail, Sir Vince said nursing his first wife Olympia as she died of breast cancer had strengthened his opposition to assisted dying.

Sir Vince Cable has called for assisted dying to be legalised in a moving article that will reopen the debate around the emotive subject

But a decade on, he had been convinced a change in the law was needed by the moving stories of constituents who chose to end their lives.

‘When Parliament finally lifts its gaze beyond the all-consuming Brexit debate, it will have to think about some of the big ethical and political issues out there,’ he writes.

‘Assisted dying is one of them.

Government should take the lead but, failing that, I am one of a growing number of MPs willing to support private members’ legislation in Parliament.’

Sir Vince said his previous objections had been based on fears that ‘greedy relatives’ could take advantage of lax laws to force elderly people to end their lives.

He warned that there would need to be ‘strict safeguards’ built in to protect the patient and the doctors involved and to prevent a ‘slippery slope’.

He said he and his current wife Rachel had decided that they would both support assisted dying if they were suffering.

Euthanasia and assisted suicide are illegal in the UK. Parliament has consistently voted against changing the law.

Mr Whaley, 80, a retired accountant from Chalfont St Peter, Buckinghamshire, wrote a letter to MPs describing his anguish at police inquiries into his case.

The motor neurone disease sufferer said his final weeks had been blighted by officers questioning his wife Ann over her involvement in his plan to end his life at Dignitas.

Meanwhile, it emerged that two people were arrested on suspicion of assisting suicide after Ralph Snell, 94, was found dead at his home in Lymington, Hampshire.

Yesterday police said that an 89-year-old woman and a 68-year-old man had been released from custody under investigation.

I couldn't let my wife suffer if her life became unbearable

Commentary by Vince Cable

One of the most difficult issues as an MP is to face a constituent who has a life or death problem and you are unable, for reasons of conscience, to help or support them.

This was the position I found myself in for most of my parliamentary career when faced with people seeking relief from a painful and distressing illness through ‘assisted dying’, or their grieving relatives.

I encountered some terrible cases, particularly people entering the advanced stages of motor neurone disease when, fully conscious of their condition, patients are – for example –unable to swallow and face the prospect of choking to death. I had to say, ‘Sorry, I don’t believe in “assisted dying”.’

Liberal Democrat leader Sir Vince Cable and his second wife Rachel in the New Forest

I have now changed my mind.

My original opposition was not based on religious doctrine, though I do respect and understand the belief that we must not devalue life itself.

My views had been formed, as they are for many people, by personal experience.

My mother died some years ago a sad and frightened old lady in her 80s, in a fog of confusion brought on by a combination of dementia and long-standing mental illness.

Vince Cable's first wife Olympia (pictured) died 14 years after being diagnosed with breast cancer

When I was in my early teens she was confined for a long time to a psychiatric hospital after suffering a breakdown – what would now be called post-natal depression (the baby being my brother).

She was pronounced cured and released and she recovered with the help of adult education which made up for the schooling she missed as a teenage factory girl.

But she was always somewhat diminished and lacking in confidence and, in her advanced years, her mental state deteriorated.

When I visited her towards the end of her life she sometimes begged to die, to be released from her unhappy state; but on other occasions she insisted on her love of life; simple pleasures like a walk in the park, and by the river.

Without self-worth, however, she was obsessed about being a ‘burden’. I could see all too clearly that, in a permissive regime for assisted dying, fragile and muddled people like my mother would easily be persuaded to sign up.

My other experience stemmed from my late wife Olympia who died 14 years after being diagnosed with breast cancer.

Her last few years with crumbling bones and loss of mobility were very difficult, undignified and painful too.

But she was a brave, resilient and positive woman who wanted to keep going as long as she could. She actually hung on until I had been re-elected in 2001, giving whatever practical help she could in bed and at the end of a telephone.

And her last wish was to die at home surrounded by her family and with their love. The whole notion of assisted dying never crossed her lips and she would have been appalled at the idea. And that confirmed my prejudice.

I have since met people who feel strongly in the opposite direction: who are not confused or mentally ill but deadly serious and consistent; who may not have the option of being at home with a loving family; who face ending their lives either in constant pain or with no dignity.

And they don’t have the money to be flown to a clinic in Switzerland.

I respond with arguments about ‘slippery slopes’ and how a system of assisted dying could be abused by greedy relatives bringing pressure to bear and overworked doctors (or worse) signing on the dotted line if asked; and how the elderly and disabled would fear coming under pressure to stop ‘being a burden’.

Having talked at length to some of the campaigners for assisted dying it is clear that these fears and reservations can be addressed: that strict safeguards can be built in to protect both the patient and the doctors involved.

There have been several attempts in recent years to change the law under which it is an offence to encourage or assist suicide (attempted suicide itself was decriminalised in 1961). Dozens of cases are referred to the police but prosecutions are rare.

The Supreme Court has declined to intervene and change the law by saying, rightly, that this is a matter for Parliament.

Recent attempts to legislate have failed but the process has established the principles and the safeguards.

Persons must have a terminal illness, medically certified. They must be mentally capable.

A judge must be satisfied that the request is voluntary, settled and informed and the signed request must be made in front of a witness and countersigned by two doctors.

Doctors would have every right to opt out of the process on conscience grounds. There is a ‘cooling off’ period for reconsideration. These considerations could be strengthened or modified.

It was striking that when the issue was last debated in Parliament there were some powerful contributions from those, like Lord Carey, the former Archbishop of Canterbury, who admitted (like me) to have changed their minds.

He said: ‘In my view it is a profoundly Christian and moral thing to devise a law that enables people, if they choose, to end their lives with dignity.’

A few weeks ago, I asked my wife Rachel – I am happily remarried – what she thought of this issue, if either of us should be afflicted by some dreadful illness. She is a humanist; I describe myself as a – rather bad – Christian.

We both agreed that if ‘assisted dying’ were legal, we could not allow the other to suffer intolerable pain should they wish to bring it to an end.

When Parliament finally lifts its gaze beyond the all-consuming Brexit debate, it will have to think about some of the big ethical and political issues out there.

Assisted dying is one of them. Government should take the lead but, failing that, I am one of a growing number of MPs willing to support private members’ legislation in Parliament.