I think it depends what you define as a "hit".
For example, Chesney Hawkes had a number one with One and Only, which was a massive hit, but not any other big hits really - but I wouldn't describe him as a "flop act". A1 and Honeyz probably aren't flop acts either, although it's been fun discussing them in the thread.
I was thinking about Kavana earlier, even though he had 2 top number 8s and a few top 20 singles I would probably call him a flop act. He never really made it big, he wasn't a household name, his songs weren't huge at the time, his songs aren't well remembered or played on the radio and whenever he's interviewed he seems to rely on his achievement of winning Best Male at a Smash Hits awards, which isn't that impressive really.
Yes, I fancied him in Corrie and in this video. I liked the follow up single too Everything My Heart Desires