One evening the following January, my brothers and I went to her bedroom as usual, one by one, to say goodnight. Relatives from Scotland had come to stay for the weekend; close friends had visited during the day. When I awoke the following morning, my father came into my room to tell me she had died. He led me to her bedside, where she lay as if sleeping. I remember squeezing her toes through the leather and wool of her slipper socks.

My brothers and I did not know that our family GP had given her the means to end her life, at the time of her choosing, until we were adults. We knew she had wanted an assisted death but not that it had been granted. Only a tiny circle of relatives and friends could be told that this was the night when she would die. Our parents couldn’t risk entrusting children with a secret that could have sent our GP to jail. My gratitude for his bravery and kindness is infinite and eternal. My only regret is that it had to be a secret.

Twenty-five years later, I sat in the lobby of University College London hospital, bouncing the 18-month-old daughter of my best friend, Charlotte Raven, on my knee. Several floors above us, Charlotte and her husband were receiving the results of Charlotte’s genetic test for Huntington’s disease. Their daughter and I were playing with helium balloons in the gift shop when over her shoulder I watched the lift doors open. They stumbled into the lobby, doubled over, tears streaming down their cheeks.

Huntington’s is an incurable neuro-degenerative disease. Like a monstrous cocktail of motor neurone disease, Parkinson’s and Alzheimer’s, it steals the patient’s mind and body, piece by piece, year by year, in an unspeakably cruel crawl to a hideous death. Inherited from a parent, its symptoms typically begin between the age of 39 and 45. Charlotte was 36 when she was told had inherited the gene.

• This disease has no class, no empathy and I know it will beat me

We’d become friends in my first year at Manchester University, where she was the student union women’s officer. Tall, model thin, with an inky gamine crop and ruby red lipstick, she wore black designer wear and quoted Derrida and terrified everyone. A vision of Marxism and Vogue in heels, I’d never met anyone like her.

After graduating, she and I shared a flat in London. She interned for the Modern Review magazine, and within months had taken over as editor. Formidably erudite, she dazzled Nineties London media land, became a columnist for the Guardian, and threw incredible parties.

Always the first person I wanted to talk to about anything, she never failed to make me think or make me laugh. She was my bridesmaid, and I was hers.

Charlotte was 41 when the initial symptoms of Huntington’s appeared. At first forgetful and clumsy, by 49 she was unrecognisable. She asked me to take her to Jamaica, on what would be her last holiday, but after falling into the hotel pool on day one, in a heartbreaking clatter of emaciated limbs, was too frightened to leave our cottage. We spent the week indoors, during which she asked me to take her to Dignitas.

• Charlotte Raven obituary: irreverent editor of The Modern Review

Anyone who imagines that it is easy to go to Dignitas is mistaken. The patient needs to produce their full medical records, but their GP may worry that in providing them they have assisted a suicide. A patient like Charlotte needs a report by a psychiatrist, stating that they are of sound mind — but a psychiatrist cannot knowingly write such a report for the purposes of Dignitas.

I spent well over a year in a bureaucratic and judicial maze, searching for a path that would expose no-one to risk of prosecution. By the time I had found one, Charlotte was no longer what a psychiatrist could definitively rule to be of sound mind.

My brilliant friend was forced to endure her final years confined to a hospital bed in her living room, spoon fed by a round-the-clock team of carers, most of whom she hated. She would text me in the middle of the night, begging me to end her life. The drugs that subdued her writhing spasms also strangled her voice. In the last year of her life, the only muffled sentence she managed to groan whenever I saw her was: “Let … me … die.”

Did she really want to? Had she been allowed the choice, perhaps she might not have taken it. We will never know. All I know is that the denial of this choice tormented her to the very end. In January Charlotte contracted an infection, and died.

When I told her last November that a majority of MPs had voted for the assisted dying bill, she gripped my hand and strained to formulate a word: “Good.” I’m glad she doesn’t know that some are now wobbling.

Opposition to the bill consists of a great deal of what-iffery. What if the elderly and infirm feel pressured? What if this bill is the thin end of the wedge? What if terminally ill people choose assisted death in a state of depression? What if, what if, what if.

These are all valid concerns that I share. But critics of the bill have begun to frame the debate as if leaving the law as it stands does not hurt anyone. It does.

They worry about speculative, hypothetical victims — but the status quo creates indisputable, real life victims. The bill’s opponents portray it as cruel, heartless and macabre. I wish they could have sat at Charlotte’s bedside, heard her groan, “Let … me … die”, and seen what cruel, heartless and macabre actually looks like. They are absolutely right that we should spend more on palliative care. But if we can’t even fill potholes, when or how is that going to happen?

The bill was debated in the House of Commons again on Friday, with MPs voting for amendments that will prevent doctors from initiating conversations about assisted dying with under-18s. But few if any of the MPs voting on the bill next Friday, which is when a final decision will be made, can know what it feels like to be told that you are dying.

Weirdly, I do. Ten years ago I underwent a double mastectomy and chemo for breast cancer. Last year I popped into my GP’s surgery, mildly puzzled by puffiness in my armpit. I was told that the tumour had returned and was in my lymph nodes. It was terminal.

I spent the next three days drawing up lists of who to ask to look after my orphaned children. I began drafting letters to them, to open on their birthdays in the years after I was gone. I couldn’t work out what to write.

All I did know, during those three days, was that I did not want to die in pain in hospital. I didn’t want my children’s last memory of me to be a delirium of morphine. I wanted to stay alive for as long as I could. But when the time came, I wanted to be able to say goodbye.

Then I had a scan in hospital, and it turned out not to be a tumour, but just harmless silicon beads that had leaked into my lymph nodes. The Physician’s Associate who’d examined me had jumped to the wrong conclusion. I wasn’t dying at all.

Although not an experience I would wish on anyone, those three days were instructive. Had the scan confirmed that it was terminal cancer, maybe as time passed I might have changed my mind. But if this bill does become law, it would have given me the choice.

We are all lucky to be alive. Those who have been told they face a painful death have already been dealt the worst luck. For the law to deprive them of any choice over how to end the time they have left is not more bad luck; it’s a choice, and it’s one that MPs now have the chance to change.

Some MPs worry that this bill is “too hurried”. They worry that it isn’t perfect. But the 1967 abortion bill wasn’t, either. Nor was the 1965 abolition of the death penalty, which wasn’t applied to treason until 1998. That doesn’t mean parliament should not have passed them. This assisted dying bill isn’t exactly the one I wanted, either. But it is the bill we have.

• Not enough time to debate assisted dying bill, minister warns

The terminally ill who gathered outside parliament last week to support it don’t have all the time in the world. When my mother was dying, I vividly recall her assuring me that assisted dying would be legal by the time I’d grown up. That was 45 years ago.