According to his owners it's only UB40 songs. They have hundreds of CDs which they play all the time, but when they put anything else on Finley just sits there in silence. "Then as soon as we put UB40 on his little tail will start wagging and banging on the floor, and then he'll just throw his head back and start yowling along. He just started singing along in his own style a couple of years ago - we couldn't believe it, especially when some of it was in tune. We were both really shocked because he's normally quite a quiet dog, it was so out of character. I think he even shocked himself slightly."
You can read the article here which includes the video of Finley howling along to "King".