Oh dear. I looked at Wikipedia and Inside BB, and it doesn't say what the ratings for TBB were so I did a little research via Digital Spy and it really was the least watched series at that point.
Episode 1, aired Monday Oct 13th 2003 - 2.5 million
Episode 2, aired Tuesday Oct 14th 2003 - 2.8 million
Episode 3 (the sex episode), aired Wednesday Oct 15th 2003 - 1.9 million
Episode 4, aired Thursday Oct 16th 2003 - 2.4 million
Episode 5, aired Friday Oct 17th 2003 - N/A
http://www.digitalspy.co.uk/tv/news/...lion-peak.html
http://www.digitalspy.co.uk/tv/news/...ex-a-miss.html
http://www.digitalspy.co.uk/tv/news/...lid-start.html
I wonder how much the finale got. The ratings were higher than BB:CH's reported 0.7 million but that's probably because of CH being exlcusive to E4 and CBB5/BB8's bad rep