One side of A4. Clear, concise.
They should be addressed to the clerk of the justices with the address of the person who is writing it at the top.
Also dated and signed.
The reference should advise in what capacity they know you and speak favourably about you. It should state how utterly out of character this incident is and how you are a respectable, honest and humble individual who is deeply shamed and remorseful about the entire episode.
It should also detail how this is an isolated incident and how they are certain nothing like this will ever happen again.
The main point I got from my solicitor was how full of humility these references should be. He advised that they can be from individuals from any aspect of your life provided they convey how mortified you are over this all.