Kate McCann: "Madeleine was in my thoughts when I woke … and as I battled to fall asleep at

KATE McCann has revealed details of the "unbearable" four years since the disappearance of her daughter Madeleine, the agony of the moment she was snatched, and her "bitter regret" for leaving her.

In a new book about her torment and fears for her missing daughter, she admitted that beneath the facade of self control - which attracted hatred and suspicion from some quarters - she was cracking under the emotional weight of her loss.

Extracts of the book, Madeleine, have been released as new reports revealed police have spoken to two convicted Scottish killer paedophiles who were in Spain, and possibly Portugal, on false passports in 2007

Mrs McCann wrote: "The appalling loss of our daughter has been too much to bear. Everything else, however huge, has had to take second place. There is only so much pain human beings can stand at once."

She admitted it "goes without saying we now bitterly regret" leaving the children while they dined with friends at a nearby tapas restaurant.

It was Mrs McCann who went back to their apartment "30 or 45 seconds away" to check on them and discovered their young daughter was missing from her bed.

"When I realised Madeleine wasn't there I went through to our bedroom to see if she'd got into our bed. On the discovery of another empty bed, the first wave of panic hit me," she said.

"As I ran back into the children's room the closed curtains flew up in a gust of wind.

"My heart lurched as I saw that, behind them, the window was wide open and the shutters on the outside were raised all the way up. Nausea, terror, disbelief, fear. Icy fear. Dear God, no. Please, no."

She said she ran to get her husband, Gerry, and the hotel management was asked to call the police.

"Gerry and I stood in the living room of our apartment clutching each other, utterly distraught," she wrote.

"I couldn't help myself let alone soothe my husband, who was in a state too harrowing for me to bear, howling for his little girl. I kept blaming myself. 'We've let her down! We've failed her!'"

She added: "I vividly recall sobbing: 'Not Madeleine, not Madeleine, not Madeleine.' Even now when the dark clouds close in on me, I find myself shaking my head manically and repeating over and over again: 'Not Madeleine, not Madeleine. Please God, not my Madeleine'.

"After that night in Portugal when Madeleine disappeared four years ago - 3 May, 2007 - it was a long time before I was able to allow myself to take any real pleasure in anything. Madeleine was in my thoughts when I woke up in the morning and as I battled to fall asleep at night."

She said they will never give up on finding her, but admitted: "When she was first stolen, paedophiles were all we could think about and it ate away at us."

New reports suggest police are investigating Charles O'Neill, 48, and William Lauchlan, 34, who were jailed last year for sex attacks on children and murdering Allison McGarrigle, and dumping her body at sea in 1997, after she threatened to report them. Neither Policia Judiciara, in Lisbon, which is leading the investigation, or Leicestershire Police, which reportedly interviewed the pair, were able to comment on the report yesterday.

No-one has ever been charged in connection to Madeleine's disappearance, and none of the reported sights since has led police to her.