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Plans for a 'super council' in Kent are in doubt after Shepway voted against the proposal.
Councillors in Dover and Thanet agreed on Wednesday night to hold a public consultation ahead of a formal merger timed to coincide with the 2019 local elections.
But the result in Shepway - where 19 out of 29 councillors voted against the plan and only eight in favour - means it may not happen.
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Councillors in Canterbury decided to abandon their vote given the result in Shepway and instead backed leader Simon Cook to "talk business" with other councils.
It was earlier stated all four authorities would need to back the proposal for it to go ahead.
The Dover vote was close with 22 for and 18 against.
Thanet District Council also voted in favour of the plan by a large majority.
But in Shepway the result was eight for, 19 against, and two abstentions.
Dover council leader Paul Watkins warned councillors that if merger did not happen, the alternative could be a county unitary.
"We are not an isolated community and if we stay isolated then the other option might be the one we least want, which is a county unitary."
He said merger would give east Kent a powerful voice to attract investment and jobs.
But Labour called for a referendum, saying voters should have a say.
"Our job is to defend the people who got us elected in Dover, not people in Thanet, Shepway or Canterbury," said Labour Cllr Peter Wallace.
The Conservatives admitted council tax bills may rise.
"There's no denying it, there would be an increase in the council tax but it's worth remembering that only 11% of bill is for Dover," said deputy leader Cllr Michael Conolly.
Speaking on behalf of the East Kent councils, Thanet District Council’s leader Chris Wells, said: "After the important decision made by councillors in Shepway, we now need to take this opportunity to take stock and work hard to find a way forward together.
"We cannot shy away from the fact there are some big challenges facing the councils in East Kent and we need to think about new and innovative ways of tackling them.
"The levels of savings we each need to achieve have been widely documented, and that position remains the same.
"We now need to identify a suitable way forward to ensure we're in the best possible position for the future of East Kent.
"We cannot shy away from the fact there are some big challenges facing the councils in East Kent and we need to think about new ways of tackling them..." - Thanet council leader Chris Wells
"Once we have gone through that process, we will come forward with fresh proposals."
Shepway Council leader David Monk said: "We will still look to see if we can't merge management across districts.
"We are probably of the four in the best position to whether a storm.
"I'm not distraught."
Councillors say the merger would save money and mean better services for taxpayers.
But some complained there were too many unanswered questions and uncertainties about how an authority which stretches from Whitstable in the north to Romney Marsh in the south would function.
Others also raised fears a 'super council' would become remote from its population and would reduce democratic representation.