When I was born, the nurses took me away from my mother before she even saw me. She “yelled the house down” until they brought me back for a brief cuddle. Then they took me away permanently. Not allowing a mother to see or touch her baby after giving birth was standard hospital procedure in 1963 for newborns going to adoption. I would not see my mother again for half a lifetime.

In March 1999, as I flew into Wellington, New Zealand, to see her after 36 years, I wondered what on earth had brought me here. What was I looking for?

After all, my life had been a fortunate one. The parents who adopted me, my mum and dad, are wonderful and I love them to bits. My childhood was spent partly in Cornwall and partly in London. My dad is the television writer Ken Taylor (Jewel in the Crown, The Camomile Lawn), my mum, Jill, is a former stage manager.

My father worked from home so we were a close family. My childhood memories are happy, so much so that I announced last year following the birth of my son Arthur that I would give up politics at the next general election so as not to be away in Westminster four days a week – to give my son the benefit of the kind of childhood I had had, to be as involved in Arthur’s (and now his brother Jacob’s) life as much as my dad was with mine.

I can’t remember not knowing that I was adopted. At school I freely told people, thinking it made me a bit more interesting. All I knew was my mother was from New Zealand and had been an art student in London. I knew nothing of my father. I enjoyed art at school and that made me feel slightly connected to her, I suppose. From time to time I imagined what she might be like, what she might be doing. And that was that for 35 years.

My adoptive parents were the only mum and dad I needed or wanted. I certainly did not want to replace them. Yet at 36 I was drawn halfway round the world to meet a “mother” I didn’t know and who knew virtually nothing about me.

Just a few months before I boarded the plane, my parents – mum and dad – suggested I saw the film Secrets and Lies. I went, trusting dad’s professional opinion, not checking the reviews, knowing nothing about it.

As I realised that they had recommended a film about an adopted woman looking for her biological mother, I remember the shock of guessing that they had guessed how I might feel. I’m not sure how they knew that it had been playing on my mind, but I had been unable to escape feeling that if I didn’t do something soon, I might never meet my natural parents.

As with many adopted children hitting their late twenties or early thirties, eventually curiosity had caught up with me. It was time to know, like the character in the film, where I had come from. Why the adoption? What would someone sharing my genes look like, think like? Do I have brothers or sisters? It was not about finding a mother or father – I had fantastic parents already. It was about finding myself.

To see my birth records I had to visit the register for births, deaths and marriages in Isling-ton, north London. A counsellor explained the adoption process; the mores of the time; the fact that my mother would probably have never even seen me and the risk of rejection should I seek to contact her. I waved aside the worries, thinking of it as looking up history.

She gave me the few pages of records. Little about my father except that he was at art college with Maggie (my birth mother), older, and it was a brief affair. But here were my mother’s communications with the agency offering me for the adoption she felt she had to sanction; sad letters and signed forms that gave me away for ever. These days an adopted child, although not the parent, can look up these records as I did and initiate contact. In those days adoption cut all contact with absolute finality.

I felt unexpectedly emotional at these handwritten and heart-wrenching echoes from my past. Then I heard the counsellor clear her throat. There was just one more thing. A couple of months ago they had received a letter from New Zealand. It was from my mother asking if she could be put in touch.

“I had a little boy,” she began, giving a few details including a name I never knew I had – Jona-thon. “Can you help me?”

They had replied confirming the bare details but telling her that she could not initiate contact. They could tell her nothing more, not even if I was alive. Her letter would be kept on record in case I ever looked her up. And here I was. After 35 years we had asked about one another within the space of a few weeks. She had written at almost exactly the moment when I was watching Secrets and Lies.

Maggie’s letter startled me and not just because of the extraordinary coincidence of timing. I had thought of all this as just history, but on the other side of the world it was plainly as raw and fresh as yesterday.

I was her baby, her only child, the son she had never known but couldn’t forget. I did not think of her as “mum”, but for Maggie I was still her baby. She had been separated from me by the social attitudes of the day. Being a single parent was never an option for her. Today, as a dad, I can imagine her pain and longing.

We drafted a brief reply. I was called Matthew, I was well, I was “in a good job”, it had been a “happy adoption” and she was welcome to write again – via the counsellor. I still held my distance from this stranger.

Her reply delivered another bombshell: “To tell you a little about me. I was born and lived most of my life in New Zealand. My father is English, and so was his father who was a Liberal MP . . .”

I was stunned. Not just the coincidence of a joint search. But here, when she didn’t even know what my job was, this extraordinary parallel with my life. Percy Harris, my great-grandfather, had – unbelievably – been a Liberal MP, just like me. Elected for Bow and Poplar in 1922, he had hung on long after every other Liberal MP within 100 miles of London had been ousted. The odds on my having followed in my great-grandfather’s footsteps in this way were minuscule.

A mother I didn’t know on the other side of the world writing to me just as I looked for her, after 35 years. My great-grandfather, like me, a Liberal MP. My world seemed to turn upside down and yet make complete sense of who I am.

I had assumed that my mother would have married and had other children. In fact, she had never married and I was her only child. I now know she had gone back to New Zealand after a – discreet – year in Australia, and as a brilliant horsewoman had taken up eventing at a high level, but was severely injured in her early thirties by a fall during a competition. Her life had not been an easy one.

At Wellington airport arrivalsI walked right past her. When I did double back it wasn’t hard to spot her: the lonely figure still hoping for one last passenger to come out after everyone had passed her. Nervously smiling– like me. This wasn’t the movies; there was no instant recognition, no immediate connection.

We hugged awkwardly, the same awkward hug that we still have when we meet, the awkwardness that speaks of the years we have missed. It took

several days before we could talk more at ease and start to explore the past.

Today we write and telephone. I care about her and I am proud of her. But don’t let anyone imagine that 36 years is an easy bridge to cross. The truth is that to Maggie I will always be her prodigal son, but to me she can never be my “mum”.

The rest of her family have welcomed me as their own. Quite something, when her two brothers were not even told about me for many years.

I especially enjoyed meeting my grandfather, Sir Jack Harris, the indomitable patriarch who flew to England to fetch back his daughter the moment he heard of the pregnancy. He opened our first conversation by telling me that he firmly opposed proportional representation. Now 102, he still writes to me about politics in no uncertain terms.

And today? Mum and dad, my adoptive parents, together with my wife and children and the brother and sisters I grew up with, are “my family”. But Maggie is now a mother with pictures of her son and her two new grandchildren on her wall.

She has visited us twice and when I was Liberal shadow chancellor she sat in the Commons for the first time since she watched her grandfather speak as a little girl, to see my response to the budget.

Mostly life goes on as before, but in a way both our lives have been changed profoundly. Maggie has her son back in her life and I have my roots – and very different ideas about what makes me who I am.

Times Recommends

• Looking for romance on the Blairs' love bus
• Children 'immersed in culture of violence'
• Hunt for black gold sweeps the country