The official BBC page, as well as the Genome 1 and 2 confirm :

• that the episode broadcasted on December 30, 2006 is the last of the 1st season and not a special episode.
• that the episode broadcasted on January 1st, 2008 is the first of the 2nd season and not a special episode.

By the way, I have also fixed the title of the series. At the time of its original broadcast, it was titled "Jam and Jerusalem" as visible on the Genome.