What is the opinion on Scarlett's accent in this film? Good, bad or adequate?
Perfectly fine. Not amazing but not terrible. She's attempting a more lower class London accent that doesn't really exist anymore. She pulls off an English accent better in The Other Boleyn Girl but she's decent enough here.
There are times when it's perfect, and times when it's ok, but it's never bad. I can't recall a time when her American accent came through- at worst she occasionally sounds like an English person with a posh/RP accent trying to do a London accent; just a general air of not fully relaxing into a way of speaking.
When I first saw this film back in 2006 I'd never heard of her before and I'm pretty sure I just accepted she was what she was playing. Too busy taking in David Bowie's new accent.