The departure of a trouble-shooter brought in to overhaul Northamptonshire's child protection services could delay improvements, it has been claimed.
Kevin Crompton is to leave less than a year after being appointed chairman of Northamptonshire's safeguarding board.
Labour opposition at the county council said the move was "deeply" concerning and could set back improvements.
The Conservative leadership said it was sorry Mr Compton was leaving.
Three Ofsted reports had branded adoption services and child protection as "inadequate", while social services and police were criticised over children being kept in cells because no other accommodation was available.
Mr Crompton helped to improve children's services at Haringey Council in north London following the death of Peter Connelly, also known as Baby P, in 2007.
'Steady the ship'
He took up the post as chairman of Northamptonshire's Local Safeguarding Children Board in a part-time capacity, but has announced he is leaving at the end of February to become director of children's and adults services at Bedford Borough Council.
Mr Crompton, who was appointed in March, said his decision was due to a "mixture of professional and personal circumstance".
"The journey isn't finished and we've always been clear it will take a good couple of years to get everything into a good state," he said.
Bob Scott, deputy Labour leader at Northamptonshire County Council, said: "Kevin Crompton was brought in to help steady the ship.
"The Labour group is supportive of positive changes, but deeply concerned that Mr Crompton's departure will delay those changes with much work still to be done."
The council said Mr Crompton had been expected to remain in his consultancy-type role for about two years.
It said he had revised child protection guidance and set up a new Multi Agency Safeguarding Hub bringing together police, social services, education and health services.
Jim Harker, Conservative leader of the council, said: "We appreciate the enthusiasm, work and real expertise he's been able to give at this critical time for us.
"We're committed to making sure we get a first-class replacement."