Lukewarm is a rotund young man with a calm and personable demeanour, who originates from Middlesbrough. The circumstances that brought him to be in prison are unknown although in one episode he successfully relieved Mr. Barrowclough of his wristwatch, in a manner strongly suggestive of a skilled pickpocket. He is known to be gay, and has a boyfriend called Trevor on the outside who is a watch repairer from Southport; Trevor appears in the episode "Men Without Women". Lukewarm shared a cell with Blanco, over whom he would fuss a lot, especially when the elderly convict was due to face the parole board. Blanco did concede that, for all his fussing, Lukewarm did keep the cell nice and clean. Lukewarm is often seen knitting.
Although he is a trusted friend and confidante of Fletcher's, he seldom becomes directly involved in his schemes, preferring instead to spend his association time observing the latest goings-on whilst busying himself with his latest knitting projects. He works in the kitchens alongside Lennie Godber and is an enthusiastic if notoriously untalented cook (although it was said that he did make good pasties).
Lukewarm was released 3 months prior to Fletcher in Going Straight. Fletcher mentions to McClaren that he has heard from Lukewarm that his court case is coming up, but it's possible he is innocent (stealing a woman's handbag, claiming he thought it was his).
In the mockumentary "Life Beyond The Box: Norman Stanley Fletcher", his real name is revealed as being Timothy Underwood, although in Just Desserts he seems to be addressed by a warden as Lewis.