My beloved 12-year-old Labrador, Cuba, was put peacefully to sleep two weeks ago.

I did not expect the grieving process to be easy, but in the long days following Cuba's death, I have found my memories of my sweet dog constantly, and disturbingly, interrupted by thoughts of my ailing, 87-year-old mother and her own deteriorating condition.

I have come to the conclusion, which I am well aware many may find abhorrent, that my poor mum deserves the dignified death that was granted to my dog. But as she's a human being - a superior creature altogether - she must be denied a gentle goodbye and continue to exist in her ghastly state of living death.

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A living death: Linda Kelsey, right, with her mother, left. Linda's 87-year-old mother has Parkinson's disease

The old idiom 'to die like a dog' was, in former times, used to express the idea of dying in degrading circumstances, or dying in a cowardly way, begging for mercy. How ironic, in the age of pampered and cosseted pets, that we do not allow our dogs to die like dogs; only people.

Here is what is wrong with my once beautiful and kind mother. For 25 years, since she was diagnosed, at the age of 62, with Parkinson's disease, accompanied by extreme anxiety and deep depression, she has been in gradual retreat from the world. Today, she lives (if you can call it that) in a state-of-the-art care home. Her teeny body, which weighs just over 5 stone, is covered in huge purple bruises and sores from blood vessels that rupture at the slightest touch, and even spontaneously.

She cannot walk, or dress, or do anything for herself, other than just about feed herself her soft-food diet, which goes everywhere, and drink a cup of tea with her trembling hand. She doesn't read or watch television. Her voice is barely audible (a symptom of Parkinson's). She is confused, with a degree of dementia.

On the upside, she recognises me and my sister, exchanges a few half-sentences here and there, and, miraculously, with major prompting from me, can still conjure up some of the answers to the Daily Mail crossword.

It breaks my heart to see her suffering, and her total dependence on the kindness of her carers.

Right from her diagnosis, it was as though my mother had given up the will to live - or at least to enjoy her life. The Parkinson's, in fact, was relatively mild compared to many others with her condition, but her anxiety and depression were incapacitating.

Linda with Cuba before he was put down after being diagnosed with suspected cancer

At least she had her dedicated and ever-supportive husband - my father Sam - to care for her and cajole her into the world.

And so for many years, albeit with increasing reluctance on her part, they continued to go to their holiday home in Spain four times a year, and my mother still took enjoyment in regular visits from me and my sister, and from her four grandchildren.

Then she fell, breaking her pelvis and her hip, and this, alongside the impaired gait caused by the Parkinson's, made walking more and more difficult.

Eight years ago, my dad - who was 13 years older than my mum, and by then 92 - became ill himself.

Linda, left, with her mother in her mid fifties, right, before she was diagnosed with Parkinson's disease at 62

The system of carers we had in place broke down, and we had to sell their home to fund nursing home facilities for them both. A few months later my dad was dead.

For almost eight years now, my mum has lived in a care home. For the first five years, without fail on my twice-weekly visits, my mother told me she wanted to die.

My mother told me she wanted to die. 'Put me out of my misery,' she begged

'Put me out of my misery,' she begged.

'Oh Mum, I can't do that, you know I can't,' I'd reply.

The platitudes I uttered about the quality of the care home felt hollow. I repeated over and over how fortunate it was that my sister and I lived so nearby that we could visit regularly, as could the grandchildren.

But all I heard was 'I want to die', 'I want to die'. I heard it so often that I began to concede - to myself but not to her - that she was right to want to die. And, for her sake, I wished that she would.

These past three years she has stopped pleading with me, but I know it's only because she no longer has the strength to muster up the words.

But back to my dog Cuba's final days. She had been slowing down for months. If, when she was a puppy, I'd found it impossible to keep up with her, now I had to literally drag her round the block.

Writer Linda Kelsey is planning to write a 'living will'

Three weeks ago, this greediest of dogs, who'd hoover up the remains of discarded chicken vindaloo containers in the park, swallow cup-cake wrappings from the gutter, and once gobbled an entire Pavlova intended for my guests, gave up eating.

I put it down to exhaustion after taking her for a longer than usual walk on a hot day, but 48 hours later she could barely walk at all and I took her to the vet, where they admitted her immediately.

Around 10pm that night, I rang to see if the results of tests had come through. She appeared to have a disease, called Immune-Mediated Hemolytic Anaemia, in which the red blood cells start self-destructing. She needed a blood transfusion.

They told me they couldn't rule out cancer. And there'd be a long course of steroids, and a big possibility of relapse. The vet said it was up to me, but euthanasia was an option I might want to consider.

The decision needed to be quick as the transfusion would have to be done within hours. I said I needed to discuss matters with my son Thomas, now 27. He no longer lives at home, but Cuba was a member of his family, and I knew he'd expect to be involved.

With a heavy heart, Thomas agreed that putting Cuba to sleep was the kindest option and insisted on coming to the vets with me.

My partner Ronny was at home with me at the time. Ronny only got to know Cuba when we met after my divorce, but he had grown incredibly fond of her and always took on the duty of the last walk at night. He wasn't going to miss out on saying goodbye to a dear companion.

No sooner had I put down the phone to my son than Thomas rang his dad (my ex), who had lived with Cuba in the early years. He, too, insisted on being there.

It was almost midnight when the four of us gathered at Cuba's bedside, where she was hooked up to a drip. Her heart was racing. Each of us stroked, kissed and talked to her in turn. She even managed to wag her tail and raise her head to look at us. Then each of us placed a hand on her, nodded to the vet, and the syringe went in. Within seconds she was gone. Not a shudder, not a yelp or a moan, just a gentle drift into the good night.

Linda at her father Sam's 90th birthday party. He took care of his wife until he died at the age of 92

We all wept. But there was nothing ugly or horrible about it. What a great way to go we all agreed. A good life and a good death.

One of the hot topics amongst my 60-something friends is that of 'living wills'. We're all planning to write them - sooner rather than later. So many of us have seen our parents go through years of needless suffering, and we are terrified of the same thing happening to us.

Even so, we know that living wills may not be enough to ease our final journey. We talk about Dignitas, too. We crack dark jokes about booking club class flights to Switzerland with the last of our savings - but that's only because we don't know how else to deal with the even darker prospects of the future.

The euthanasia debate is difficult and contentious and deeply personal. There are those who argue that loosening the laws on euthanasia would greatly increase the risk of people who want to live being killed.

Linda's parents at their wedding, 1947. Her mother was 20, her father 32. They were married for over 60 years

They would also argue that the danger of violating the right to life is so great that we should ensure euthanasia remains illegal at all costs.

I know only this: that I wish my mum - as I would wish for myself in similar circumstances - could die exactly as Cuba did. With a doctor at her side to send her peacefully away, and my sister and me there to smile and hold her and kiss her farewell.

If it were legal, I'd do it in a heartbeat. I would grant her the request she made when she had the words to express it. I would not recoil in horror. I would not feel guilty. It would be a sad blessing.

Soon, I will receive Cuba's ashes following her cremation. There are plans for a family picnic on Hampstead Heath, Cuba's favourite playground, where she'd run for hours, swim in the pond, roll for joy in the mud.

We will scatter her ashes and talk about all the pleasure she gave us and know that we gave her the death she deserved.