The role of Daniel Cleaver (Hugh Grant) only had a very small appearance in the book. The character was so memorable and popular that his part was extended specifically for the movie.
Plans to have George Clooney appear in a cameo as himself were dropped.
The poem Daniel quotes to Bridget on the boat while in Thailand is a translation of the famous "Phra Aphai Manee", a famous epic poem about a hero/ prince who, among other things, wooes and marries many princesses. The part he quotes is when Phra Aphai Manee wooes his head wife, Suwan Malee.
The book that Jed and Shazzer read on the plane is "The Beach" by Alex Garland that also partially takes place in Thailand.
Giles Benwick, whom Bridget meets at the law council dinner, shares his last name with a character from Jane Austen's "Persuasion".
Bridget makes a comment about Mark wearing a wet shirt. Colin Firth made a famous scene playing Mr Darcy in "Pride and Prejudice" (1995) where he appeared to Elizabeth Bennet in a wet shirt after swimming in a lake.
In the book, Bridget Jones is obsessed by the actor Colin Firth from the BBC TV series "Pride and Prejudice" (1995), and even gets to meet him for an interview. This plot-line is omitted from the film, where Firth actually plays her love interest Mark Darcy.