Funny, I listened to the score for this about week ago -- the original with Marti Webb -- the first time in years. I thoroughly enjoyed it, particularly the Dance portion.
I was traveling regularly to London on business when the London production was open. Since it was in the theatre at which Les Mis opened in 1986, I saw it at least 32 years ago, four times; which is amazing, because I generally preferred to spread the wealth among as many productions as possible.
I so loved the original production -- particularly the Dance portion -- that I kept returning. There was a grittiness to the entire production, no sets other than a platform that reminded me of the set piece for the staging of The Girls Upstairs in Follies, just some stairs on a platform as I recall.
Even though I have always loved BP, i pretty much hated the New York production. The sets (backdrops?) in Song were horrible, and the stage just seemed too small for Dance (plus the choreography was inferior (seemed too 'sleek' instead of the grittiness of the London staging). To me, the two parts always belonged together, and they just didn't seem part of a whole in NYC.
That said, while I think the score is very good, I just don't think Tell Me On A Sunday is interesting enough to be presented on its own in a theatre. Re the suggestion of extending it to full-length (I assume at least 90 minutes), IMO it is just not substantial enough to begin with...and that padding would only serve to highlight that fact; further, how many people are going to be able to sing a 90 minute production 8 times a week, etc.?
Maybe as a performance piece at a cabaret -- where the tickets are reasonable and you have a drink in your hand -- but the singer would need to have a lot of presence for it to work.