The reference should be:
preferably one page but no more than two
neatly written or typed
addressed to The Chief Clerk
signed and dated
The referee should include:
their name and occupation
how long they have known you
how they know you
their opinion of your character
any examples of matters demonstrating your good character
their opinion of the pending matter
any other relevant matters

The referee should not include:
their opinion of the appropriate sentence.
anything false or something they are not sure about
anything they would not be happy seeing printed in a newspaper