By Character Reference I am presuming that they mean a Personal Reference... something like:
Date
To whom it may concern
I confirm that I have known (name) for (number) years.
(State relationship - social, business, working together in some other capacity, club, activity, project, etc.)
At all times I have found (name/him/her) to be (state characteristics - eg, dependable, reliable, hard-working, conscientious, honest, peace-loving, courteous, etc).
I'm happy to provide further information if required. (optional)
Yours faithfully, etc.