It was the middle of a cold November night and Carl Lygo was preparing the car to drive his wife, Faye, who was in labour, to hospital. He switched on the engine of their Range Rover, put on the heating to warm the inside and spread some towels and blankets on the seat where Faye would be travelling. Somewhere in his mind was a terrifying thought … but no.

Too unlikely.

Ten minutes later, Faye, by now on all fours in the back of the car as it sped along the A28 in Kent towards Ashford maternity hospital, had the same thought. Like her husband, she dismissed it. Soon afterwards, Carl asked if she'd like him to head instead to a midwife-run birth centre five minutes' drive away, she told him – between contractions – to stick with the main maternity unit. The baby was big – if there were complications, she wanted to be in a hospital with an obstetrician.

As it turned out, the only complication was having to stop the car. A few miles further down the road, Rex Sebastian Peter Lygo, weighing 9lb 7oz, was born on the back seat.

And Carl just kept on driving – just as he had four years earlier when their daughter Scarlet was born on the same stretch of road, in almost identical circumstances.

"When I tell people I gave birth in the car twice, they can hardly believe it," says Faye, 39. "The odds against it must be immense."

The Lygos' first two children, Max, 10, and Alex, nine, were born in hospital: but Alex's birth wasn't without drama. Two days beforehand, Faye was in a serious road accident and ended up in a field; the car was a write-off. "The police said we were very lucky to escape unscathed. I had a night in hospital and then came home, only to return in labour two days later," she says.

Both older boys' births were fairly long and drawn-out, so when Faye went into labour with Scarlet, Carl, now 46, was pretty confident there was no great rush. "It was the middle of the night so I knew we'd have a clear run. I thought we'd get there and it would be a couple of hours before the baby was born," he remembers.

But as the car went over a bridge, Faye felt an unmistakable urge to push. "I was facing the back window and the headrest gave me something to hold on to," she says. "I didn't tell Carl how far along things were because I didn't want to worry him."

The first indication that the birth was imminent was when Faye announced she could feel the baby's head. Another push and a moment later Faye was lifting Rex up from the gloom of the back seat. "Carl heard me say, 'Hello, sweetheart,'" she recalls.

Gripping the steering wheel, Carl realised he'd have to make a decision about whether to stop or keep going. "It was a dark, country road, and I didn't think I could help much by pulling over," he says.

"I thought, best keep on going because if there are any problems, we need to get to where there's medical help. I'm a lawyer and have dealt with medical negligence cases so I know the sorts of things that can go wrong at a birth. As well as all that, Scarlet wasn't making any noise.

"It was quite a nerve-racking experience. I was aware that I had to drive extremely carefully, but also knew I had to be pretty swift in case of a problem with Faye or the baby."

Faye takes up the story: "He was saying, 'Have you slapped the baby? Have you cleared her nose? Is she definitely breathing?' And then he asked me if I could find the hospital's phone number! Fortunately, I'm pretty organised and I had it right there on the front page of my notes so, holding the baby with one hand, I dialled the hospital with the other and explained.

"They said to come straight to the ambulance bay at A&E, where a crash team was waiting."

A few minutes later, the couple arrived at Ashford hospital, and Faye and Scarlet were whisked away. "Then I had to go to find the car park and pay for the parking," says Carl. "It's funny how you still have to do these mundane things in the midst of something so momentous."

When Faye found herself pregnant again three years later, this time with Oscar, there were plenty of jokes among their friends about getting to hospital on time. "We'd moved to Canterbury by then, where we still live, so we knew it was going to take longer to get to Ashford," says Faye.

"I went into labour at about 5.20am and we knew we'd be up against it with the rush-hour traffic, so we took no chances and went straight in."

By the time Rex, now three, was on the way, the memory of Scarlet's back-seat arrival had receded – yet, says Faye, as she waited in the early hours for her parents to arrive that morning to look after the other children, she had a growing sense of deja vu. "I kept thinking, this is so like Scarlet's arrival all over again," she says.

"And when I saw the way Carl had put the blankets and towels all over the back seat of the car, I knew it was in his mind as well.

"It seemed like for ever before my parents turned up, then I remember being hardly able to get out of the house and into the car. A few minutes into the journey, Carl had the idea of going to the midwife-led unit at Canterbury, but I said no – press on. It was only about five minutes later that I realised, oh my goodness – it's going to happen again. Then I thought: well, I've done it successfully once. I can definitely do it again."

Interestingly, Faye says the second car delivery was more frightening from her point of view – while Carl says it was easier. "Because of Scarlet's arrival, I was so aware of all the things that could have gone wrong that time – I knew I was facing them all again."

She recalls: "When Rex was born he was still in the caul, or membrane, and I remember thinking, what do I have to do about this? Fortunately, with the next push they broke so I didn't have to do anything. And when he was out I wrapped him up straightaway because Scarlet had got a bit cold by the time we got to the hospital, and I didn't want that to happen again."

What made Rex's birth better than Scarlet's for Carl, he says, was that his son made plenty of noise when he was born.

"I could hear him loud and proud, so I knew he was OK," he says. "We had quite a leisurely drive to the hospital after that, talking about how we were going to clear the mess off the back seat. And, of course, I knew exactly what to do – go straight to A&E – because I was an old hand.

"But when I started phoning people up to tell them about it, no one could believe it had happened again. It just seemed incredible … it still does."