‘Why do you think you didn’t see him?” It’s so obvious but it comes like a kick in the belly. The words hang in the air and I stare at him blankly. Why didn’t I see him? That’s the great unanswered and unanswerable question that has haunted me for months.

“If I knew the answer to that …” I say. Tears well yet again. They come instantly these days.

“Was it because you were dazzled, perhaps? The driver coming towards you flashed his headlights …”

Is he leading me on, offering a neat escape? He’s cool and practical, this police officer. The other one speaks less but smiles more. They are doing their job, getting the facts and sifting the evidence before deciding whether to prosecute me. After all, a man has died. Someone must be guilty.

“No,” I say. “I don’t think I was dazzled.” It matters hugely to me that everything is rigorous, scrupulously honest. Whatever the findings, there must be no hint of deception, no room for doubt.

It’s April 2016, four months after the accident. This limbo will hold me in its grasp for another six months, until the inquest takes place.

I had always loved driving. Before I was old enough to learn I would sit on the cracked red leather seat of Dad’s Austin Cambridge, pretending to change gears, negotiate traffic, double-declutching on steep hills. Mum had learned to drive on tractors in the Women’s Land Army during the war. She taught Dad, my brother, my sister and finally me. At 17 I passed the test, bought a Morris Minor for £200 and went on to relish the freedom of the open road for 40 years. For my 60th birthday my treat was to spend three weeks driving from New York to San Francisco with no planned route, making it up each day.

I pulled over, shouting, 'No, no!' I understood at once nothing could be the same. Lives had changed in those seconds.

On 31 December 2015, I was in Norfolk for a Christmas break, enjoying the big skies and windswept cliffs. I drove a couple of miles to take someone a thank-you gift and decided to head into the town of Holt for a bite to eat. The cafe closed at 5pm and I made sure not to stay to the last minute, aware that the staff would want to clean up and get ready for parties. I was planning a quiet evening with a glass or two of prosecco. Nothing out of the ordinary. That’s how my life looked: predictable and comfortable.

By 5pm it was as dark as night. I headed east out of Holt and swung round the righthand bend, preparing to join the A148, the bypass. From a side road a small car nipped in front of me and slipped into a space in the traffic. Someone’s in a hurry, I thought.

I turned left on to the main road, and began to move up through the gears. That’s when a car coming towards me flashed its lights. This used to happen to me a lot in the Mini. So much that a couple of years earlier I’d taken it back to BMW to get it checked; yes, my headlights were wrongly adjusted and I had inadvertently been annoying other drivers. So when this driver flashed, I instinctively flashed back: “No, those aren’t my main beams – these are, see?”

The time between my flash and the impact was infinitesimal. And yet in that moment I glimpsed a face in the road. It had a look of incredulity, as if saying, “What the hell are you doing?” The moment was so brief. From seeing that shape, a hunched outline against the black of the night, to the sickening smash was instantaneous. No time to react, to respond, to brake.

I pulled over, shouting, “No, no, no!” I understood at once that nothing could be the same. Lives had changed in those seconds. There was a figure lying on the road. One or two people were around it. Nobody spoke. Or if they did I couldn’t hear. I spat grit from my mouth; later I understood that it was fragments of glass from the shattered windscreen.

“Has someone got a phone? Have you called for an ambulance?” I was shouting. Why didn’t anyone reply? I couldn’t go near the body; I was terrified of what I might see. My legs gave way and I slumped to the kerb. A woman touched me on the arm. It felt the kindest thing ever. But then she said, “Don’t worry. It’ll be all right.” And I knew that was a lie.

‘He couldn’t bear to sit around with the others watching the telly’ ... the programme for a celebration of Michael Rawson’s life. Photograph: Alicia Canter/The Guardian

Police arrived in minutes. I was led to sit in one of their big vehicles and an officer, who introduced himself as Jason, asked me questions. He wrote my words down laboriously and asked me to sign my statement. My hands were shaking so much I couldn’t hold the pen. Eventually I scrawled my name on the paper. I blew into a bag, had a swab taken from my cheek. My phone was examined; had I been texting or making a call? No, the last message was from my friend Marian when I was in the cafe. Something banal, back then, a world away.

I was taken to a shop where a kind couple made cups of tea for me and all the police. There seemed to be so many of them now.

“The air ambulance has taken him to Addenbrooke’s,” a policeman called Bob said. “But he’s not in a good way.” There had been a helicopter?

“Why do you think you didn’t see him?” I don’t know, I don’t know! It was dark, he was wearing dark clothes. “Was I dazzled?” I don’t think so. “Had I been drinking?” I doubted myself. Perhaps I had. No, I’d had a coffee. “Was I distracted, tuning the radio?” No, it was off. My car: were the lights working? Yes, they had been checked. The tyres, the brakes … Everything was as it should be. There was no explanation. Two years on, there is no explanation. No way to make sense of it.

“Who can come and collect you?” Bob asked me. “A family member?”

Instinct said I wanted my mummy and daddy. Both dead. My boyfriend – well, my ex – was in Canada. My best friend was in France, my sister in Shropshire, my brother in Ireland. I shook my head, lost.

“Or a neighbour?”

Nuala, next door, was 80, frail and didn’t drive. There was no one who could help me, take this horror away, kiss it better.

The call came: 'Michael Rawson didn’t survive.' There is no way to describe the anguish of hearing those words

I had two friends who lived an hour away. A call was made. John and Laura arrived, wrapped me up in a blanket to take me away. On the journey to their house I began to feel nauseous and John stopped the car so I could be sick. It was a visceral heave, my guts wrenching and churning. Again and again the muscles strained and squeezed involuntarily. Then came the yawning. Huge, ridiculous gulping movements beyond my control, the jaw stretching until it was painful. In any other context this would have been comical.

I stayed with John and Laura for several days; mostly I lay in bed not sleeping.

I was numb with shock and pain. They talked to me; I heard some of the words. One day I put clothes on and stepped five paces outside into the garden. It felt like an achievement. I sat in a wooden chair until I was cold and then retreated inside. I felt so fragile, totally vulnerable. As if I had lost a layer of skin.

It was while I was at John and Laura’s that Bob called. The man I hit was in his 70s. He had a name now: Michael Rawson. He was in hospital and was “critical but stable”. I imagined him immobile, tubes and machines keeping him alive. And I allowed myself to picture us meeting, me carrying flowers to his bedside, distraught with apology. Or would we be angry with each other?

“What were you doing?”

“I could ask the same of you.”

“You flashed me. I thought you’d seen me and were letting me cross the road.”

“I flashed the other driver.”

Whatever the dialogue, the scene assumed that he would live. But six days into the new year the call came: “Michael Rawson didn’t survive.”

There is no way to describe the anguish of hearing those words. There was no chance to undo it. I had become a killer. A death is always huge. But others I had witnessed had been after illness – cancer, dementia – and there had been a dying process of months or years, a chance to be involved, say farewell, make adjustments and prepare for the end. The brutality of this was hell.

To be responsible for someone’s death is an unimaginable position. There are so many questions. All the what-ifs of leaving the cafe a minute earlier or later, of glimpsing the man in the road in time to avoid him, of his pulling through and recovering. But they are fantasies.

“It wasn’t your fault,” I was told so many times. “It could have been any one of us.” I wouldn’t wish this on my worst enemy.

“What do I do with this?” I had asked John on the night of the crash. “I don’t know,” he had said. “But you will.”

A week or so into January, when I was able to function again, I went shopping for new clothes, all black, as a mark of respect. “Are you in mourning?” someone asked me, thinking they were making a joke. I said, “Yes,” and the conversation ended. I stopped shaving because it seemed an insensitive self-indulgence to pay attention to my appearance. I had therapy; a lot of therapy. In those sessions I cried until I thought I’d never stop. I became terrified of crowds and loud noises, cowering against a wall and blocking my ears if I heard a police siren. I’m still claustrophobic and panicky in enclosed spaces. I can’t cope with any gathering of more than a handful. I wait on kerbs for the green man to show before crossing, even when there is no traffic. No risks must be taken.

I chose half a dozen people to tell. Each time I related the facts I dissolved. I gripped one friend’s hand so tightly I damaged her fingers. The shock was identical every day, endlessly repeating. I went to see my doctor. He signed me off work, handing me a slip of paper that referred to post-traumatic stress disorder. Me? Surely not. I’m the strong, resilient one.

The weeks passed, the seasons changed. Eventually the date of the inquest was announced: 28 October. My solicitor said that as I hadn’t been called by the coroner to give evidence I shouldn’t attend. But my instinct told me I needed to be there, to hear the summing up, to witness this public reckoning.

‘Yes, Michael would have been angry with you. But then he would have forgiven you,‘ one of his friends told me ... the order of service for Michael Rawson’s funeral. Photograph: Alicia Canter/The Guardian

People talk of closure. But for me, the inquest was the opposite: the feeling of something that had been gripping me tightly around the throat opening up and allowing me to breathe again. “No blame should attach to the driver” were the words I’d waited 10 months to hear.

The following day I shaved off my beard and consigned my black garb to the back of the wardrobe.

A few weeks later I asked Laura if I could visit her and try to drive again. I wept as I began but the mantra of “I can do this … I’m a good driver” allowed me to sit at the wheel for half an hour and pilot her car around the country roads.

Freed from the limbo I knew there was more I needed to do. I contacted the residence where Michael Rawson had lived. He had got off the bus and was crossing the road to go home when the accident happened. I was fearful of animosity; after all I was the driver who had killed one of their friends. But my fear was ungrounded; I was welcomed with kindness and empathy. And laughter – something I had denied myself. I began to learn about Michael the man and his character.

“He was a proper rogue!” I was told. “He would take risks. Despite having two strokes he was determined to live his life. Even in the winter, with snow on the ground, he would struggle into town for an Indian or a Chinese meal. He couldn’t bear to sit around with the others watching the telly.”

I learned that Michael had studied at the same university as me, but 15 years earlier. His profession of linguistics took him around the world; he had lived in South Africa and Canada. His passions were photography and classical music. He had a vast collection of CDs and would invite friends to listen to his favourite composers for hours at a time, educating them as he shared his excitement.

I was shown a photograph of him, with a bemused half-smile on his face. I felt as if I was being introduced to him, meeting the man I had killed. I said, “Hello.”

Others imagined my meeting him too. “You’re like him in many ways. You’d have had interesting conversations.”

As I heard about him from his friends, Michael came alive to me. Yes, it’s ironic but that’s exactly how it seemed: he came alive. No longer merely a death, a statistic; he became a man who lived a full life.

One of his closest friends told me, “I was angry with you when I heard what had happened. But the police said you hadn’t been drinking, weren’t speeding or using your phone, and my anger dissipated. Michael would have been angry with you too. Oh yes, he’d have been very angry. But then … he would have forgiven you.”

What a kind but bizarre offering. The idea that Michael would forgive me for killing him. This friend even took me to the woodland burial plot where I was able to spend time saying the things I needed to express. To apologise, of course.

And now, two years on? I am aware of Michael every day, aware of his death and my part in that. But also of the existence before my car ended his life. The PTSD continues in unexpected ways. I’m still hypersensitive to noise, anxious in crowds. I cry at the tiniest prompting, often at kindness and evidence of a shared humanity.

But I’m angry too. When I see pedestrians texting as they cross the road I shout at them: “Don’t be stupid! That’s so dangerous!”

I struggle daily with the riddle of how to go on living as the person I have become. To be The Man Who Killed, or not be defined by that one event? Throughout those almost unbearable days, did I ever consider that taking my own life would be the right thing to do? No. In fact the accident has given me an urgent duty to live a more worthwhile life, and in doing so to honour Michael Rawson. That responsibility I bear willingly; it will be with me always.

• Meeting the Man I Killed will be broadcast on BBC Radio 4 at 8pm on 10 April and 5pm on 15 April. Jonathan Izard is donating his fee for this article to Brake, the road safety charity – he has also created Accidental Death as a space to share stories of personal healing and recovery following the trauma of a road traffic accident.