On IMDb this pilot episode listed as two-part Season 1 https://www.imdb.com/title/tt1333192/episodes?season=1

Wikipedia elaborates a bit:

The pilot, also sometimes referred to as a "Christmas Special", was first broadcast in two parts on BBC Two.[1] On 24 March 2003 the pilot was released on a DVD on which the two parts were edited into a single 100-minute film, removing more than 20 minutes of footage from the original broadcast.[2] The U.S. release of the DVD, for which the series was retitled Dr. Bell and Mr. Doyle, followed in 2006. It retains the original two-part format.[3] — source