Madeleine McCann Photo: PA

Kate McCann felt like committing suicide in the weeks after her daughter Madelaine vanished from a holiday apartment in Portugal four years ago, she has disclosed

The little girl was three years old when she was abducted, having been left alone with her brother and sister, Sean and Amelie, while their parents dined with friends nearby.

Her mother realised she had been taken as she made the latest of a series of half-hourly checks. The bedroom window was open, with the shutter having been raised from the outside.

In a new book to mark the fourth anniversary of her daughter's disappearance, Mrs McCann recalls running outside, screaming: "Madeleine's gone! Someone's taken her!"

Later, she sank into fits and anguish and depression that eventually threatened to destroy her relationship with her husband, Gerry.

She writes: "I had an overwhelming urge to swim out across the ocean, as hard and as fast as I could; to swim and swim and swim until I was so far out and so exhausted I could just allow the water to pull me under and relieve me of this torment

"I wasn't keeping that desire to myself, either. I was shouting it out to anyone who happened to be in the room. Both this urge and the expression of it were, I suppose, an outlet for the crucifying anguish.

"Somehow, inflicting physical pain on myself seemed to be the only possible way of escaping my internal pain. The other truly awful manifestation of what I was feeling was a macabre slide show of vivid pictures in my brain that taunted me relentlessly.

"I was crying out that I could see Madeleine lying, cold and mottled, on a big grey stone slab. Looking back, seeing me like this must have been terrible for my friends and relatives, particularly my parents, but I couldn't help myself."

Her inner torment contrasts with the widespread public perception, and particularly on internet forums, that at the time she seemed remarkably composed.

The reality, she insists, was that she had gone into shock.

"It's quite frightening when I see myself in those early days," she says. "To me I look incredibly fragile and confused and lost."

The failure by Portuguese police to trace either Madeleine or her abductor condemned the McCanns to a life of unrelenting torment. In Kate McCann’s case, this was punctuated by flashes of how she imagined Madeleine might be suffering.

"It was a long time before I was able to allow myself to take real pleasure in anything. I couldn't watch television, read a book, listen to music ... How could I possibly take pleasure in anything without my daughter?"

The new book has been written to raise money for the ongoing Find Madeleine campaign. Madeleine’s siblings are now aged six.