If you agree to provide a reference, you're obliged to be honest, fair and reasonable, both for the candidate and for the potential employer. Stick to truthful, job-related information, ideally based on actual documentation, such as performance reviews and job description. Factual information helps potential employers make an appropriate recruitment decision.
Providing references about current and former employees makes it easier for them to advance in their careers.
If you have been asked for a written reference, and are not sure how to structure your response, see the useful tools section on the Checking references page.
If you feel unable to be a referee for a current or former employee that you supervised, or if you have concerns about the content of a reference that you are preparing, you may wish to discuss the situation with your Divisional HR Manager or Adviser.