A woman who drowned her three-year-old daughter in the bath to prevent her estranged husband from having contact with the girl 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.

Michael Colebourn said after the sentencing that he missed being a father to a “special little girl” who brought joy to family and friends.

“My beautiful daughter has been taken from me in such a cold and callous manner at the very hands of the one other person that should have protected her and kept her safe,” he said.

“Throughout the trial, I and all those that loved Bethan have had to endure the heartbreak of listening to her last moments. I have also had to suffer endless unfounded allegations and lies made against me with no opportunity to respond.

“I desperately miss being a daddy, we would have such great times together. Bethan’s laugh was infectious and her energy was endless.”

Bethan died at the family home in Fordingbridge, Hampshire, in October 2017. Afterwards, Colebourn, 36, 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.

The jury was also told Colebourn wrongly suspected her husband, 38, was having an affair with a colleague at the marine company of which he is chief executive.

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 had 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.’

Karim Khalil, defending, described his client as “a woman in emotional turmoil” and said she never sought to deflect attention over what happened to her daughter.

Jailing Colebourn for life, the judge, Ms Justice Johannah Cutts, said: “She [Bethan] was clearly a beautiful little girl who was full of life. She had everything to live for. You were her mother, you were responsible for her care and her wellbeing.”

The judge said Michael Colebourn left the family home as he felt it was the best decision for the three of them.

“What followed was a period of emotional difficulty for you,” the judge said. “You were an emotional rollercoaster; one moment you were trying to get back together with Michael, one moment you were trying to divorce him.

“Mostly, you felt keenly betrayed; you became convinced your husband was having an affair and tracking you in your house. There was no evidence this was the case.

“Bethan was your child and you were her mother, you had responsibility for her care and wellbeing. The fact you even considered killing her should have shocked you.”

• In the UK, Samaritans can be contacted on 116 123 or email jo@samaritans.org. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is 13 11 14. Other international suicide helplines can be found at www.befrienders.org.