The character played by Daniel Craig, had no name in the movie. The movie, is based on a book of the same name Layer Cake, and the protagonist (character played by Daniel Craig) has no name there too. He is Anonymous in the book.
If you read this interview of the director, Matthew Vaughan, you would know that they gave a name to this anonymous character, for the movie. Quoting the below part from that interview
It's an interesting character for him to play, isn't it? This man with
In the book he's just anonymous. But in the script it's really weird.
We didn't want to give him a name, but you have to call him something
in the script, so he became "XXXX". The last line of the book is the
last line of the movie. The studio wanted to cut it, but I told them
it was really important. The fact that he doesn't have a name is what
makes him so different. He's Clint Eastwood, riding in on a horse, he
doesn't give anything away. He's a chameleon.