Boris said I could bring up his daughter. Then the texts and phone calls began...

erty business were being frozen by lawyers acting for a Middle Eastern client wanting to know what had happened to tens of millions of pounds. Pierre denied any wrongdoing but, with his firm placed in administration, he would eventually relocate to Canada and, as he put it, ‘start from less than zero’.

I felt awful for Helen: she’d had no option but to flee her home less than a month after giving birth.

‘Pierre was always on a plane doing deals or sitting on another charity board,’ she continued. ‘One moment he was in New York, the next flying into the World Economic Forum in Davos.’

At the mention of Davos, Helen took a gulp of wine and looked away. ‘You know that Pierre may not be the father,’ she said.

I nodded, saying: ‘Pierre is dark, like you.’

‘The identity of Stephanie’s father cannot get out. The father was calling me at the hospital.’

‘Does Pierre know who it might be?’ ‘He has an idea,’ she replied. ‘How did he take it?’ ‘He’s having a paternity test. We both knew our relationship wasn’t working. In fact, it was over.’

Helen was used to dealing with whatever life threw at her. She’d had a triple family tragedy: her sisters, Enid and Stephanie, and her father had all died within a few years of each other when she was growing up in Kent. She had shown steely resilience throughout and had never lost her self-deprecating good humour. You could tell her anything.

She also had an almost complete lack of reserve or guard when it came to talking about men, love, politics and sex. She loved risqué texts and louche Paris clubs and casinos. I had never met anybody else of such unaffected candour.

After lunch, I walked her to the Mini. As she stood by the car, I kissed her beside a parking meter. (Yes, she had a ticket). There felt nothing surprising about this.

When she grabbed the ticket, she laughed and walked towards her new home. As she waved back, I knew another chapter in my life was about to begin.

IT WASN’T long before I was spending much of my time at her home off the Kings Road. I was happy again, even when she finally told me the name of Stephanie’s real father.

Alexander Boris de Pfeffel Johnson was probably the last person you’d want as a rivale d’amour. Two years older than me, he was a heavyweight champion when it came to conquests, a veteran swordsman and super-hack paid £250,000 a year for one newspaper column (which he described as ‘chicken feed’).

I felt as if I’d been pushed out into the hot glare of the Circus Maximus to fight a seasoned gladiator.

I had met him only a few times but knew enough to know he craved attention. I’d been to a party at the Spectator magazine where, as the then editor, he’d jumped on to his mahogany desk to make a speech. It juddered under his weight. I couldn’t imagine his predecessors playing the ‘editor-showman’ in such a way.

I’d been relatively ancient, in my mid-thirties, when I got engaged to my first wife. Boris, in contrast, was engaged while still at Oxford to aristocratic model Allegra Mostyn-Owen. She later left him when he embarked on an affair with barrister Marina Wheeler, a childhood friend who became his second wife.

I had no personal problem with Boris. He’d known my family for years as my father, Eurosceptic MP Bill Cash, had been at Oxford with Boris’s father, Stanley.

I’d long known that Helen was a fan; she had the entire Johnson oeuvre of books on a shelf beside her bed, from his comic political novel Seventy-Two Virgins to collected journalism.

Yes, I was jealous of Boris’s hold over the woman I loved, but such were his political ambitions that I thought the likelihood of his leaving Marina was remote.

For the moment, all I wanted was to be with Helen, and if that meant bringing up Stephanie as my own daughter – preferably as her stepfather – then I was 100 per cent fine with that.

It was now critical that everyone in the tight family circle who knew the truth of Stephanie’s father had to be bound by a code of omertà. Nobody could talk about it, not even so much as hint.

For myself, I feared being burned alive by the fire storm that would destroy anything, or anybody, within its range if the news were to break.

WITHIN a month or so, I had pretty much moved into Helen’s cottagelike house in Markham Street.

From the outset, I never made any secret of the fact that I wanted to start a family with her.

If we had our own children, nobody was going to know (or care) that the eldest had a different biological father. Helen did not seem averse to this idea, and she was a brilliant mother.

The other good news was that, as the works proceeded at Upton Cressett, Helen started to get involved. I had taken her to Shropshire within weeks of us starting to see each other. She had a natural decorator’s eye and was soon helping source items for the house.

She seemed to love Upton Cressett, even if it were still mostly a building site. Instructions soon followed for buying a complete set of Fissler cooking pans (in Harrods’ sale). I was to consider only Miele dishwashers and washing machines and so on. But I was happy to do anything that led to us moving in together.

Yet rumours about the identity of the father refused to stop humming. After two months or so, it was decided between myself, Helen, her mother and stepfather that we needed a ‘Boris Summit’ to tell him of our intentions.

‘You will have to meet him,’ I said, ‘and tell him about us.’ ‘Tell him what?’ ‘That I’m going to bring up his daughter whether people know the identity of her father or not.’

‘Don’t you think you should come as well?’ asked Helen.

‘No,’ I said. ‘This is between you and Boris. Tell Boris that I’m in love with you and that I’m very fond of Stephanie and that I want to bring her up in Shropshire. And that within a few years or so, when we’re married and have our own children, nobody is going to know that they’re not all our own children. He can come up and stay whenever he wants to see Steph.’

So Helen went off to meet Boris at Brown’s Hotel in Mayfair, alone. As I waited at her house, I had a surreal vision of him becoming part of the extended Cash family, with long Sunday lunches washed down with rosé as he discussed politics with my father. Maybe Boris would arrive in a bullet-proof Jaguar with a police detail.

The ‘Boris Summit’ at Brown’s was a long meeting – worryingly so. Helen was away for at least two hours. After the second hour started, I began to think I was a fool for having suggested a swanky hotel. Thankfully, when Helen finally came back, she looked perfectly normal. ‘Boris is fine with our plan,’ she said. ‘He’s fine with you bringing up Stephanie.’

Boris told her he knew about Upton Cressett as he’d been there for a political house party in the autumn of 1995 at the invitation of my father and my mother, Biddy, who used to work at Downing Street. ‘Biddy, I love Biddy. Will Biddy be there?’ Boris had exclaimed to Helen.

He thought Upton Cressett would make a perfect home for Stephanie, conveniently out of the London public glare. I was already thinking of buying an engagement ring. We were all going to be one glorious, extended happy family.

The only problem was this: if the identity of the father got out, our plan was likely to blow up.

By now, Helen and Pierre had the results of the paternity test proving Pierre wasn’t the father and, against this background, our life started to feel as if a slow-burning fuse had been lit beneath it.

By the end of June, the Boris factor was inescapable. Helen and I had been at a Swiss art fair when she stepped outside the exhibition

A heavyweight love champion, Boris was the last person you’d want as a rivale d’amour Boris is fine with you bringing up Stephanie,’ Helen told me