Diana Coad had represented the Langley St Marys ward on Slough Borough Council since 2007
Diana Coad, a Tory supporter for almost 50 years, has represented the Langley St Marys ward on Slough Borough Council since 2007.
She said she had found it “increasingly difficult” to support Mr Cameron.
“It has taken a lot of angst and a lot of crying to come to this decision,” she said.
The Conservative Party has declined to comment.
Councillor Wal Chahal, deputy leader for Slough Conservatives, thanked Mrs Coad for her past contribution and support and wished her well in her new party.
“We are a party made up of local Slough residents, who were born and raised in this town and we will continue to fight for the needs of those who live in Slough,” he added.
Labour-led Slough Borough Council said it was looking into whether Mrs Coad’s resignation on Thursday affected any of the authority’s committees.
Mrs Coad, 63, said: “It’s got nothing to do with my former colleagues locally, it’s the party nationally.”
She added: “I’ve been in the wilderness since Cameron was elected. I have tried very hard to support him but I have found it increasingly difficult.
“Our infrastructure is crumbling under the sheer weight of numbers of people in this country, and people are continuing to come,” she said.
“Someone has to address this issue without being called racist.”
She said she had “no issue” with immigrants, adding: “I have friends from every nationality.”
Mrs Coad would have been a Tory supporter for 50 years in March.
“When I was a teenager I used to hand out Conservative leaflets in the East End of London, despite my parents both being Labour supporters. I really have left my political home.”
A UKIP spokesman said the party was “delighted” with her decision.