The Search For Nicola Bulley, which will air on BBC1 on October 3, reveals the huge tensions between the police and Nicola's family prior to the discovery of her body.
Lancashire Police were criticised by politicians, including then Prime Minister Rishi Sunak, for telling the public that Ms Bulley was suffering from 'specific vulnerabilities'.
In the statement it said she had 'suffered with some significant issues with alcohol which were brought on by her ongoing struggles with the menopause and that these struggles had resurfaced over recent months'.
At the time, the force defended the 'unusual step' by saying it had needed to give more detail 'to avoid any further speculation or misinterpretation'.
The Sun reports that Mr Ansell, who had been with Ms Bulley for 11 years, reveals in the documentary how the police released a statement while the family were looking over it to make amendments.
'We were in the living room, still working on it and before we knew it they had released it,' he recalled.
'Nikki would be mortified about what has happened and how it came about.'
He added: 'There was an awful lot of conflict with the police.'
In the documentary, Detective Superintendent Rebecca Smith, who was in charge of the case, claims Mr Ansell was 'key to a lot of people's theories and we had to negate that'.
Ms Bulley vanished on January 27 last year while walking her dog Willow along the River Wyre in St Michael's on Wyre, Lancashire, shortly after dropping her daughters off at school.
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