The singers, who were together in Atomic Kitten for six years, both went to Liverpool night club Kingdom on Thursday but apparently sat at different tables and failed to converse.
"They've always been so close - especially after they both fell out with Kerry Katona when she quit the band. Yet they didn't acknowledge each other once. It was very strange," a source told The People.
McClarnon and Hamilton reformed the group with Jenny Frost earlier this year, although their comeback single failed to chart.