peter3053, I'm with you on most of your points, but I do have to disagree about Ken Jennings. I believe in real life he has a rather thick Irish accent, and what he did in SWEENEY TODD was a variation on that. To my ears, he sounds more lower-class English SWEENEY, but with an Irish tinge. Anyway, I certainly think his accent is appropriate for that character in that world at that time.
Not to belabor this, but what bothers me a little (not a lot) about Merle Louise's accent on the cast album (and in the show, when I saw her in it live) was that she was obviously TRYING to do a cockney accent, and not succeeding, whereas Cariou, Lyndeck, and some of the others made no attempt at any sort of Brit accent.
As for your comment about what Sweeney's accent would be if someone were to attempt it, clearly Johnny Depp agreed with you that it should be cockney :-)