A former employee, let's call him John, asked me for a written reference letter for a job he was applying. I was not particularly happy with John’s performance while working for me and also how he left my company with very little notice. I decided to write the reference letter for John and let him know what I really thought about his time working for me. I was honest, I didn’t exaggerate, some of it was positive, but I did state that in my opinion his performance was less then adequate and I would not hire him again. I wrote the reference in an email and sent it to John (only to John). Last week John got in touch, he told me that my reference letter cost him the job and that he was going to sue me for defamation. Is this possible? Can I be liable for defamation if I give a former employee a less then favourable written reference? I only sent the letter to John and I didn’t actually expect him to forward my letter on to his new prospective employer. Should I be concerned?