Needless to say, I was astonished. Leo's birth had seemed like a miracle, and here I was nearly three years older. Although the idea was daunting, to say the least, I realised that it would be nice for Leo not to be what amounted to an only child. As before, I went to see Susan Rankin, who arranged for me to have a scan in-house.

The radiographer was in raptures. “I have never seen a baby in a mother of your age that wasn't conceived by IVF,” she said. Tony was less enthralled. “I'm not sure I want to be a father at 50,” he said.

This time we decided to say nothing to anyone about the pregnancy. Not Alastair, not Fiona, certainly not Gordon. Not even my mum and dad. Only Jackie and the children knew. Unusually for me, I wasn't feeling at all well. It was going to be a hard pregnancy, I realised, and I was feeling grim most of the time. In fact the Mirror published a picture of me sitting down after an official photo with the Queen during a lunch at the Guildhall, part of the Jubilee celebrations. I'd been standing up for the picture, but then had felt incredibly weak. Needless to say, this was taken as proof of how rude I was, and how anti-monarchist, the caption being something like “Cherie snubs Queen”.

On August 5 we were back at Chequers. As I had a conference at Matrix [her chambers] on the morning we were due to leave for France [on holiday], I had taken advantage of being in London and booked myself in for my next scan. It was the same radiographer as before, and she was really excited, going on about how rare it was for someone my age to have a naturally conceived baby ... she was just moving the sensor across my oiled stomach when suddenly she stopped.

The truth about Tony and Gordon

Cherie Blair reveals her husband is advising Gordon Brown but says he did not trust him enough to stand down early

• 'The problem with me and Gordon is nothing personal'

• Cherie Blair: motherhood, makeovers and making ends meet – my life in Downing Street

• Cherie Blair: the secrecy and sadness behind a remarkable memoir

Multimedia

• Full coverage: Cherie Blair autobiography

BACKGROUND

• My complex life in Downing Street

• Secrecy and sadness behind memoir

• Leo: my miracle baby at 45 (and yes, he did have the MMR jab)

• The night I hated Tony

BACKGROUND

• Miscarriage: ‘I'm afraid the baby's dead, Mrs Blair'

• The Queen and I: relations with the royals

• Cherie Blair's face-off with Campbell over Caplin

• Peter Foster and the ‘scandal' that never was

Related Links

• Leo: my miracle baby at 45 (and yes, he did have the MMR jab)

• Tony Blair used Cherie's grief to protect Iraq strategy

• The night I hated Tony

Multimedia

• Alpha Mummy: How does your husband compare?

“There's no heartbeat,” she said, still staring at the screen. For a moment I didn't understand.

“What did you say?”

“There's no heartbeat, Mrs Blair. I'm afraid the baby's dead.”

“Ah,” I said. “So that's why I'm feeling better.” Because I was. After the storm that night at the Commonwealth Games, the nausea had disappeared. I told her I needed to go to the loo. She pointed me to one immediately off the room, and the moment I sat down the bleeding started. Later I thought it was almost as if, now that I knew, my body could let go.

By the time I emerged from the cubicle Dr Rankin had appeared. They were going to have to do a scrape - a D&C - she said. She would call Zoë Penn [a consultant obstetrician]. “We'll try to get you in and out as soon as possible.” Nobody need know. For the time being, I should go back to Downing Street and rest.

I stood numbly by the door in the waiting room and the detective came over. “Come on now, Mrs B, no dawdling. You've got that holiday to think of. Can't have you missing that flight.”

“I don't think I'll be going on holiday,” I said. I felt embarrassed. He didn't even know I was pregnant, and I didn't know what to do or say. “I need to speak to the PM.”

“Are you all right, Mrs B?”

“Just get me the PM, and take me back to No 10.”

The flat was empty and silent ... I walked upstairs suddenly feeling very, very old, and crawled between the sheets and just lay there, strange sounds ringing in my ears. Only when Tony got through did I let go.

He said he'd come up to London straight away, after explaining things to my mum and the kids. Twenty minutes later he called back. The kids were OK, and he hoped I understood, but he had to tell Alastair. Ah, yes. Alastair. I lay there just waiting. Then the phone again: this time the two of them on the line. There were implications in not going on holiday, they said. It was known that we were going to France. It was all to do with Iraq. There had been talk that we might be sending troops in. If we didn't go on holiday, the concern was that it would send out the wrong messages. They had decided that the best thing was to tell the press that I'd had a miscarriage.

I couldn't believe it. There I was, bleeding, and they were talking about what was going to be the line to the press. I put down the receiver and lay there staring at the ceiling, as pain began to grip.

Finally Susan Rankin rang. I should get to the hospital as soon as possible - Chelsea and Westminster, where I'd had Leo.

When I began to come round from the anaesthetic and was being wheeled out of the operating theatre, who should I see but Gary, one of the detectives. He was looking so distressed that I burst into tears, sobbing and saying, “But I really want my husband”. In fact Tony was there, but because of the security issues it was Gary whom I saw first.

As for Tony, his main emotion appeared to be relief. “You know you felt there was something not quite right, Cherie,” he said. “So it's probably all for the best.” I realise now that he was simply trying to make me feel better; it just came out a bit oddly. Of course, he was right, but I was surprised at just how badly it hit me.

It wasn't as if I was childless. I had four lovely, healthy children. But I was overwhelmed by this great sense of loss. To me, more than anyone else, this baby was real. I had seen it. I still have the scan.

Speaking for Myself is published by Little, Brown on May 15, at £18.99. ©Cherie Blair 2008

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