It's almost five years since I was walloped on the head by a police van while crossing the road. Careless? What can I say, m'lud? The van was on the wrong side of the road. But that kind of detail faded into irrelevance. What immediately mattered was that my life had all but gone. I lost consciousness and fell into a coma. When I came round days later in a hospital intensive care unit, I had lost my memory. So I had in effect lost my identity. I had been a radio and television presenter. I was suddenly all-but-dead meat.

So who am I now? Who's writing this account? Neurologically, that's a reasonable question because for days and weeks and months of my life, I wasn't there. A year ago, I began to wonder... where was I? Who was I?

Gradually, I've pieced together what happened to me and learned a little about what identity depends on and what makes me who I am. And I've relied on the help of family and friends and strangers to try to understand where I went. Many people have held a piece of the jigsaw, some who knew me before the accident, some who did not and for whom I was a hospital number.

Tens of thousands of people experience traumatic brain injury every year. The lucky ones recover, but many do not and every case is different. It is impossible to generalise about brain-injured people, save for one detail: recovery takes a long, long time and is sometimes rapid and easily observed and sometimes infinitesimal.

Nearly five years on, I feel ready to describe my journey, in the hope that it may help others to negotiate the boggy swamp of recovery. For a long time, I wasn't interested in looking back. As I slowly returned to a semblance of normality, I had no interest in examining the dark days. A friend said something which became my mantra: 'The only way is forward so forward we go!'

What eventually provoked my initially hesitant exploration was the interest of documentary maker Roger Graef, who persuaded BBC4 and BBC Scotland to commission a TV film following my progress. I started on what I hoped would be safe ground: the first person to see me in intensive care, in a cage of wires and tubes providing breathing-support and draining the fluid from the pneumothorax in my chest, was my brother, Rod. I'd seen him during my slow recovery, but never asked him what he had seen and how he had reacted. What he and his wife, Diane, said shocked me.

'Your head was totally swollen and blue,' he said. 'It looked like a huge blue pumpkin. Your eye was halfway down your face. And you had a big hole in the side of your head, above your eye.'

I didn't know what to say. Appearance matters. How we look to ourselves and to others is an important element of our identity. 'I didn't think you'd make it,' he said and Diane nodded.

'You shouldn't have survived,' she said. 'I'll never forget how you looked.'

I said I started on safe ground. The safest ground seemed to be my loyal partner, Allan, who stuck by me. This is not typical. Many husbands, wives and families of brain-injured people decide their partner or relative is fundamentally not the same person. Allan had shown extraordinary patience in seeing me through the bad times. Now I was in effect liberating him by asking him to tell me the truth - and it hurt.

'You looked as if you'd been whacked with a baseball bat,' he said. 'I didn't think it was you when I came into intensive care. I thought there'd been a mistake. I didn't recognise this bloody mess on the bed. Your face was enormous, swollen and discoloured with red and blue patches, and your eyelids were a violent, distressed crimson. Your chest rose and fell to the pace of the ventilator. Wires were taped to your face, hands, arms and chest. Black and green screens were measuring your heartbeat, blood pressure and breathing. And then I recognised your feet. And your hairline.'

Who was that? Could that be me? After some days, I began to recover consciousness, by which I mean someone began to mumble odd words, but it wasn't me. I have no recollection of the weeks that followed. I rely on the memories of others.

So Allan remembers asking me if I was in pain and my saying: 'Yes.'

'Where does it hurt?'

'Everywhere.'

Now I remember neither that conversation nor the pain. Apparently, I didn't remember who Allan was. I guessed he was a doctor or a childhood sweetheart. Tests suggested I'd lost years of my life, memory-wise. I didn't remember that my grandmother had died 20 years earlier. I didn't know Princess Diana was dead.

I had even forgotten how to swallow. So I wasn't allowed to eat for week upon week and was kept alive via a nasal feeding tube. This ensured survival, but also weight loss. Before I was deemed ready to attempt easy liquid intake, my weight had gone down to seven stone, a drop of more than 30lbs.

Alas, I have no memory of being so fashionably thin, just as I have no recollection of being a swollen, multi-coloured bruisefest. In fact, my self-awareness was in abeyance for years. This is, apparently, a typical consequence of brain injury. The medical term for it is anosognosia. Anosognosia refers to a psychological deficit. Your usual self-monitoring systems are not operating. In my case, this affected my behaviour in different ways. For a start, my appetite-control was shot to hell, so as the post-accident months and years passed, not only did I regain the weight I had lost, I put on a further four stone.

I had never had a weight problem in my life. I hadn't particularly liked chocolate. Now, I'm told, I wolfed down box after box of chocolate and fudge and absorbed fish suppers. My response to my vague awareness of not being able to get into familiar clothes was to buy bigger sizes. Meanwhile, I was chronically fatigued. Having graduated from a wheelchair to being able to climb stairs without exhausting myself, I remained in need of excessive amounts of sleep. Every day, I slept in the afternoon, and I don't mean the tipsy European siesta kind of nap, but a heavy two or three hours in bed.

Another typical symptom of brain injury is aphasia, or word-finding difficulty. I suffered this to a worrying degree. For someone whose working life depends on words and articulateness, losing the ability to use that basic tool of humanity - speech - was a serious flaw. Allan encouraged me to play different kinds of word games to develop different facets of my linguistic weakness: Scrabble, which he felt aided my concentration; Boggle, to accelerate the speed of my word-finding skills; and crosswords, to develop the lateral thinking which a sophisticated facility with the English language relies on.

Allan's reward for his steadfast support and care was bleak. I became dependent and possessive to an obsessive degree. I now know, because he can now tell me, that I was hard to live with. I was getting bigger and bigger and more and more self-centred. I've apologised to him since. All I can say in response to his chastening disclosures about aspects of my behaving badly is: 'But I wasn't there! That wasn't me!'

Looking back, it seems miraculous that he stayed with me. And I know that if he had walked away, my recovery would have been partial at best.

Of course, formally, my recovery is partial. I consulted the medical profes sionals who had cared for me. My neuro-psychologist, Gail Robinson, was uncompromising. 'Given the severity of your injuries,'she said, 'I would not expect your recovery to be full.' My London consultant, Dr Richard Greenwood, was even starker in his analysis: 'The length of time that you suffered post-traumatic amnesia means that you are indisputably a different person. It is not possible to withstand change.'

Conventional neurological wisdom insists that I am a different person. I find this hard to accept and hard to understand. I suppose that the obstinate Scots/Yorkshire anti-authoritarianism in me refuses to conform to conventional wisdom of any variety. So a current ambition is to become a medical footnote.

So who am I now? Am I a cunning simulacrum of the woman I used to be? Possibly. Am I, to borrow a doctor's unusual codification, 'a walking miracle'? Probably. I still am a hospital-number. Repair-work is still in progress. A year ago, anosognosia abated and I began to look in mirrors again... and didn't like what I saw. I embarked on a strict regime, which is steadily reducing my weight. I asked my GP to refer me to a plastic surgeon in the hope that he would smooth out my crumpled face. He examined me and expressed doubt as to whether the original lifesav ing work could be improved on - but said he'd have a go.

After the operation, I looked very bruised again for a couple of weeks and then recognised myself. He had done an excellent job. He thinks he can improve on it, so I have one final session under the knife soon. I never thought I would ever volunteer for cosmetic surgery, but vanity is part of human nature.

So, five years on, a stranger meeting me would never guess what I've been through and I see no profit in mentioning it. One abiding consequence of the accident is that the world sees me through a biased prism. Given how little the experts understand about the capabilities of the brain to restore itself after trauma, it is not surprising that the wider world worries that brain injury may lead to a permanent reduction in intellectual capabilities. For many sufferers, it does. For me, it means I have to paddle all the harder to make a living.

It is impossible to generalise about brain injury and neurology may never hold all the answers to the puzzles of identity and consciousness. Philosophers teach me as much as scientists in my quest for understanding.

What is the ultimate lesson I've learned? That our identity relies to a great degree on other people and friends and strangers can be heroically generous. And that the only way is forward - so forward we go.

· Who Am I Now? BBC2 Scotland, tonight, 8pm; Storyville: Who Am I Now? BBC4, Tuesday, 9pm