A second Oxfordshire councillor has lost their seat after failing to fill out the correct paperwork.
Conservative Patricia Bosley won 539 votes in the local election on May 1 to win a seat on Didcot Town Council, then went abroad on holiday without having signed a declaration of acceptance.
Colleagues realised she had been caught out by the technicality when the council met for its annual meeting and mayor-making ceremony on May 12.
She automatically lost her seat under rules in the Local Government Act 1972, leaving the council with 11 Labour members and nine Conservative.
Town Clerk Julia Underwood was left with no option but to advertise a vacancy.
In Witney, Dr David Morton also failed to sign his acceptance form because he was with his mother following the death of his father and lost his town council seat.
Electors in Didcot now have until June 9 to request a by-election, which would cost the town council about £2,000.
If less than 10 people want one, the seat will be filled by co-option, whereby members would decide who should join.
John Flood, leader of the Conservative town councillors, urged voters not to call a by-election so that money could be saved.
He said: "It's unfortunate, but she was a new councillor and didn't know the law.
"It would be silly to have an unnecessary by-election."
District returning officer Steven Lake, who organises elections, said that once the matter came to light, legal steps had to be taken.
He said: "It's fairly unusual for it to come to my attention."
Mr Lake added that Ms Bosley would be free to stand again at a by-election and there was nothing to stop her being co-opted.
Ms Bosley is understood to be caravanning in France and was unavailable for comment.
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