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 jokingly relieved Mr. Barraclough of his wristwatch in a manner strongly suggestive of a skilled pickpocket. He is known to be gay. He has a boyfriend called Trevor on the outside who is a watch repairer from Southport and who appears in the episode "Men Without Women". He shared a cell with Blanco. 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.
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.