Julie Mockford, who represents East Grinstead – Baldwins on the district council, will continue to serve as an Independent.
Mrs Mockford said she made her decision after hearing a woman who was ‘incandescent with rage’ start to cry while speaking on the radio about her brother’s funeral.
The funeral was held on the same day as one of the alleged parties – which are now under investigation for Covid rule breaches.
She added: “She had been unable to join fellow mourners following the service as gatherings were not allowed.
“I felt a surge of anger in my stomach – I went straight to my desk and tore the membership certificate in half.
“I let them know at headquarters – rather amusingly I received an email saying that, due to higher volume of emails at the moment, their response might take longer than normal!”
Mrs Mockford also serves on East Grinstead Town Council where she will continue to represent the Baldwins ward as an Independent.
She said her decision to leave the Conservative Party ‘feels good’, adding: “It has been a while coming, if I’m honest – but I slept well last night.”