Lucy is Smithy's girlfriend. Lucy is never seen in any of the episodes but she is always being mentioned by Smithy. We get the impression that Lucy is a young girl of about 16-18 years old due to some of the comments Gavin's family say about her and the activities that Lucy does. Smithy says she is "17 and three quarters" in series one, and "18 next week" in series two (which is consistent with the time gap between the two series). She is always involved in some sort of activity that is usually associated with younger, fitter people. Smithy always has excuses for Lucy like saying "if Lucy wasn't doing her D of E this weekend I would have brought her", "she's washing cars with the brownies" or "she's been grounded for 2 weeks".
In the first series, it could be thought that Smithy was just pretending to have a girlfriend, however in Series Two, Episode One, it is confirmed that Lucy exists when Gavin mentions having met her twice, once at a funeral.
Pam makes a comment about Lucy saying "she never stops that girl".
In series two, she cheats on Smithy, giving him gifts and sweets to soften him up before telling him.