I saw Pet Clark in concert several years ago and she was superb. Although I wasn't a big fan at the time, I was accompanying a friend who was.
Oddly enough, I thought the weakest songs Petula sang were her hits. Her renditions of various other songs in jazz, blues, etc. modes were absolutely brilliant.
"Tell Me It's Not True" (from 'Blood Brothers') was a show-stopper.

I'm now 'a fan' :-)