Exeter and Norwich each lose 13 councillors
Twenty six councillors in Exeter and Norwich lose their seats after a High Court decision over unitary status.
Mr Justice Ouseley last month quashed a Labour government decision to allow the cities to take over county council powers and now members must stand down.
Chief executive of Norwich City Council Laura McGillivray said they would ensure the council still ran smoothly. Exeter said the process was "botched".
Each council lost 13 councillors and was ordered to pay legal costs.
The 26 councillors were due to stand for re-election in May but had been granted extensions in office as part of provisional arrangements for unitary status.
The judge has now ruled the by-elections must take place to maintain legality.
Chief Executive of Norwich City Council Laura McGillivray said in the light of the decision, the council was considering the implications for the executive and the make-up and balance of the other committees on which the 13 councillors concerned served.
"I would want to reassure people that we will be making every effort to ensure the council runs smoothly in these unusual circumstances," she added.
'End of matter'
Exeter City Council leader Adrian Fullam said: "The process for considering Exeter's unitary bid has been botched from start to finish.
"Now people in Exeter face a set of emergency elections. This is an expensive and arguably unnecessary solution to a problem which should not have arisen."
The judge agreed while the cities were "not themselves to blame for the pickle, it would be quite wrong for the court to stay its hand in the light of the unlawfulness".
The judge was asked to allow councillors to remain in office until by-elections could be held in May next year.
The judge replied that course, "whilst tempting", would raise a number of technical legal difficulties.
"Really the only option is to quash the orders", he told London's High Court.
"That is an end of the matter."