Since most British TV series only produce 6-12 episodes a year, popular TV shows produce special Christmas episodes. Lovejoy had two special double length episodes.
The Prague Sun (1992) - Lovejoy is alone for Christmas. But when a friend is attacked, Lovejoy and Eric are off to Prague on a treasure hunt. And Lady Jane shows up to help out. Guest Donald Pleasance and Peter Vaughn.
The Lost Colony (1993) - Lovejoy has relatives from America visit. But when some Sir Walter Raliegh antiques disappear, Lovejoy has to go to Carolina. But when he gets into trouble, his new love interest Caroline comes to his rescue. Guests Barbara Barrie, Ken Kercheval and John Gielguld.
Lovejoy was an iconoclastic series in England and had a strong following in America. The show was uniformly excellent. The Prague Sun is definitely the better of the two episodes.
The one thing to be careful is that these episodes do not appear on another series DVD set. (i.e. the As Time Goes By retrospect special was released seperately, then released with the Series 7 dvd!)