Ruth (portrayed by Julia Morris) was an Australian friend of Kate. Ruth was always the more professionally successful, which made Kate a bit jealous and the only thing she held over Ruth was the fact she was in a stable relationship.
She came to visit Kate in London after Kate's breakup, however Kate had failed to tell Ruth about it. So instead Kate convinced Lee to pretend to be Tim. The pretense worked, even after one of Kate's friends spilled the beans. However, it all fell apart after Tim visited the flat pretending to be Lee. Ruth revealed that she thought Kate had a crush on Lee as he was the one she always talked about to her, causing Tim to reveal the deception.
Ruth was upset at Kate for lying but forgave her before she left. ("Aussie")