Sally Clark paid an emotional tribute to her husband yesterday after the Court of Appeal quashed her convictions for the murders of their two baby sons on the grounds of fresh evidence that he had uncovered.

Lord Justice Kay said he had no doubt that the convictions were unsafe after hearing that a pathologist withheld medical test results that suggested one of the babies could have died from a rare bacterial infection.

From behind the bars of the dock, Clark looked across at her husband Stephen, sitting in the public gallery. Her face crumpling into tears, she mouthed: "I love you." He smiled back and raised his arms in victory.

Three years and two months earlier, when she was convicted at Chester Crown Court, Mr Clark had whispered the same words to his wife as she was led away to begin a life sentence for smothering or shaking to death their sons, Christopher, aged 11 weeks, and Harry, eight weeks, within 14 months of each other.

From then on, he vowed to prove she was innocent. As Clark, a solicitor, walked out of the door leading from the cells a free woman, her husband clutched her in a silent embrace.

Later, on the steps of the court, Clark, 38, her voice cracking with strain, said: "We are not victorious. There are no winners here. We have all lost out. We simply feel relief that our nightmare is finally at an end."

But Clark reserved an emotional expression of gratitude for her husband, with whom she has a four-year-old child.

While he clasped his hands on her shoulders to steady her, she said in a whispered voice: "He has stood by me and supported me throughout this whole nightmare, not through blind love or unthinking loyalty, but because he knows me better than anyone else and knows how much I loved our babies.

"He has been my rock and I love him now more than ever."

After one unsuccessful appeal, Mr Clark, a 40-year-old City lawyer, discovered vital medical evidence which had been withheld from the prosecution, police, defence and jury by Dr Alan Williams, the Home Office pathologist who carried out post mortem examinations on both babies.

It was evidence which the Appeal Court said yesterday would have changed the course of the trial. When the Crown said it was not seeking a retrial, Clark was given her liberty.

Lord Justice Kay suggested Dr Williams would face severe criticism in his written judgment and the General Medical Council said it was looking into his role in the case.

"We were waiting for the outcome of the appeal case and will move to our next stage now," said a spokesman for the GMC.

Outside court, Clark also thanked her friends, legal team and inmates at Bullwood Prison, Essex, for showing "unwavering and unconditional support". She also praised the parents who have written to her in their hundreds, many sharing "very personal memories and painful experiences".

Of her father, Frank Lockyer, a retired police commander, she said: "Despite my innocence there have been times when I have felt that I have let him down in some way. Yet he has stood by me. . . I only hope he is proud of me today. I am certainly proud of him."

Mrs Clark, who is likely to be awarded compensation of hundreds of thousands of pounds, appealed for privacy so that she and her husband could "grieve for their little boys in peace".

She was charged with murder following the sudden death of her second son, Harry, in Jan 1998. Fourteen months earlier, her first child Christopher had died suddenly at home and when Harry died, medical staff called in the police.

The convictions were quashed after the Appeal Court was presented with a medical report discovered by Mr Clark in Nov 2001, which showed the presence of the staphylococcus aureus bacteria in Harry's central spinal fluid.

In addition it revealed the presence of a higher than average white to red blood cell ratio and polymorphs - cells which fight infection. All suggested that Harry, rather than being the victim of a non-accidental death, could have been suffering from a rare form of meningitis.

But Dr Williams kept this report "secret" and it was only when Mr Clark threatened the hospital with legal action that he discovered it in his son's records.

Lord Justice Kay said he would give full written reasons later, but ruled: "The jury were deprived of the opportunity of hearing and considering medical evidence that may have influenced their decision."

Earlier, the judge said he did not believe the pathologist had withheld the evidence maliciously. But he invited Dr Williams to court yesterday to explain his actions. The pathologist declined.

The Law Society said it would not stand in Mrs Clark's way if she decided to resume her career as a solicitor.

Despite being convicted of murder, she was suspended rather than struck off by the Solicitor's Disciplinary Tribunal in 2001.