In a report published last week, the committee criticised the decision of the authority's Conservative administration to abandon the partnership, which was quoted in the council's comprehensive performance assessment as an example of good practice in partnership working.
The council made the decision to recover control over highways functions in September. But district councils disagreed with the calculation that the change would save £1 million, arguing that it would cost them more.
Maidstone Borough Council has estimated that unused office space and overheads would cost it £200,000. The report states that if the other 11 district councils face costs at only half this level, the additional costs to the taxpayer would still amount to £1.3 million.
Maidstone council leader Mick Stevens insisted that most district councils want to continue the partnership and develop it further, but their views are being ignored. "I genuinely do not know why the county is doing this," he said. "The supposed savings are not going to be forthcoming."
The report also points out that many district councils will no longer want to pay to subsidise highways functions once they have been denied a role in running the highways service.
But Kent County Council leader Sir Sandy Bruce-Lockhart said that Maidstone's claim that it would cost the authority £200,000 goes against what its technical officers said in a report issued in the summer. The change has already taken place in other parts of the country, he added.