Officials who missed chances to save murdered baby Preston Davey should face a police investigation into possible negligence, a former Home Secretary has urged.Jack Straw said a public inquiry into how the 13-month-old was sexually abused and killed by adoptive father Jamie Varley, 37, would take too long.The former minister believes the threat of prosecution would encourage officials to ‘think better of their public responsibilities’ and be less susceptible to be ‘taken in’ by lying adults.After secondary school head of year Varley was convicted of murder on Monday and his partner John McGowan-Fazakerley, 32, was convicted of causing or allowing the death of a child, it emerged there were eight chances to save Preston.Serious questions are being asked about the scrutiny faced by the middle class couple, who lived in an immaculate home in Blackpool, Lancashire.Preston’s grandmother Debbie Davey has suggested officials may have been reluctant to intervene in case they were branded ‘homophobic’. She has called for social workers to be sacked.Over a period of four months, 'pure evil' Varley and McGowan-Fazakerley physically, psychologically and sexually assaulted the child under the noses of social workers and hospital staff.Varley was said to have treated Preston as his 'plaything' when left alone with him for long periods as McGowan-Fazakerley, a sales executive for a finance firm, travelled for work.