Claire Colebourn, left, and her daughter Bethan Image Credit: Supplied

A woman who drowned her three-year-old daughter in the bath to prevent her from having contact with her estranged husband has been jailed for a minimum of 18 years.

Claire Colebourn, a former biology teacher, said she drowned Bethan because she believed she would be "safer in heaven" than with her husband, Michael.

Colebourn, 36, also wrongly suspected he was having an affair with a work colleague at the marine company of which he is chief executive, a court was told.

Bethan died at the family home in Fordingbridge, Hampshire, in October 2017. After drowning Bethan, Colebourn, who has diabetes, tried to kill herself. She denied murder but was convicted by a jury at Winchester crown court.

In the witness box, Colebourn claimed her husband "hammered" her emotionally and would not let her and Bethan "be at peace".

She wept as she told the jury she thought the only way to keep her daughter safe was to kill her and ensure she could not be anywhere near her father.

"When your emotions are being hammered by somebody so much and you see your beautiful little girl suffering as well because she feels for her mummy," she told jurors.

"She's going to be a lot safer in heaven than she is anywhere near her father. The spirit can be at peace then, and Michael would not let us be in peace. I would walk to the end of the earth for her."

When asked by the prosecuting barrister, Kerry Maylin, what she had intended to do to Bethan in the bath, Colebourn said: "I can't use the words you want me to. She was going to be safe, because she would be in heaven. Bethan was going to pass into heaven."

Before the murder, Colebourn researched drowning on the internet and looked for information on churches and cemeteries. Bethan's body was found the next day in a downstairs bed, her hair still wet.

Confessing to police, Colebourn said Bethan told her she did not want a bath. "She went to the bathroom, saw the bath running and just said: 'I don't want a bath mummy, I don't want a bath,'" she said.

"I have never been so stressed in my life. Then I drowned my daughter; I drowned my own daughter. It's going to haunt me for the rest of my life. Her whole body jumped after holding her for a while.

"She didn't fight against my hand. Her arms were tucked under her. I think sadly, very sadly for her now. She had complete and utter trust in me, didn't she?"

In his closing speech, Karim Khalil, defending, described his client as "a woman in emotional turmoil".