The party won 33 seats on Thanet District Council, Kent, in May, making it the first authority in the UK to have a UKIP majority.
UKIP councillor Jeff Elenor announced on Tuesday he was defecting to join the Democratic Independent Group. He joins four other UKIP councillors who defected last month saying they were unhappy with the council’s lack of action over Manston Airport.
They also said they were unhappy about what they felt was insufficient focus by the council on issues such as housing, mental health and disabilities. Mr Elenor said he did not feel the council was fulfilling its election pledge on Manston.
In May, UKIP won 33 seats, the Conservatives 18, Labour four, and independents one – 29 seats were needed for a majority.
UKIP now has 28 members, but remains the largest party on the council.