Does my Head Look Big in This is narrated by Rebecca Macauley. She does a pretty good job but cept the character of Cassandra starts with a cockney accent then goes all BBC World News in the next chapter.
This might be because of an inconsistency in the text. Cassandra describes herself as having a difficult to understand cockney accent - then in the next chapter she says her parents moved in "high society" in England and her father was a banker, following in the footsteps of his father and father's father.
Possibly I'm just full of terrible stereotypes and don't understand how many third generation cockney bankers there are moving in London's high society. But Macauley definitely changed Cassandra's accent. Perhaps this was deliberate to try to match the text and then she just hoped no-one would notice. Well, ha! no such luck, with Penny the Pedant in town.
In general, Macauley's accents are solid, with the exception of the cockney, which is bloody difficult - look at Mary Poppins.