|Portrayed by||Olivia Caffrey|
Tamsin is Oliver's Irish ex-girlfriend, who left him for unknown reasons around six months prior to the beginning of the fourth season, and has since become pregnant by another man, with whom she has now split. She befriends Susan at an antenatal class and is also revealed to be one of Patrick's many ex-girlfriends. Tamsin and Oliver seem to have a sour relationship, as is shown over the three episodes in which she features. She refers to him as a cross between brother and sister.