Don't judge the London run of anything as a success. They run shows forever over there, even when they are mediocre.
I think the Stephanie Lawrence version or Kiki Dee is best. There is also a version with Barbara Dickson which is good. The mother needs to have an extremely powerful voice to pull this show off.
Even though I like the show, there are a couple of problems with it.
Grownup actors play children. If not done properly, it can really be annoying.
The Marilyn Monroe motif goes on too many times. When the mother compares her jailbird son to Marilyn Monroe, it's a little much.
One of the themes of the story is difference between the classes, which is felt more in Britain than in the U.S.
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.