I'm not a lawyer but you still need to be careful what you write about people. BN's post reads more like an allegation than an opinion.
A solicitor's advice follows.
In today's world broadcasting defamatory material on television, or publishing it on the internet via Twitter or any other medium is permanent and constitutes libel.
Examples of defamatory statements include allegations of:
•Fraud
•Dishonesty
•Being investigated/under suspicion of a crime
•Racism, homophobia, or sexism
•Guilt
•Sexual crimes
•Mental illness
•Avoiding debts
Allegations of mental illness may be defamatory if they have an impact on the victim's ability to conduct his or her profession or calling.