Well, though I fell at the second hurdle of sustaining a dialogue of much meaning, I can report that I successfully floored anative Welsh speaker from Cardiff, who literally dropped her jaw in disbelief when I asked her if she spoke Welsh. She was completely phased by someone English speaking "her language" (in a good way) especially by my gog accent.
What made the difference to me was meeting another group of native Cardiff people who were about as anti-Welsh as I have ever met. I think I know who writes to the Western Mail!