My question involves defamation in the state of: United kingdom.

My subordinates at work have written letters of complaint to my senior Manager claiming that I was being racist to them, also stated that I treated them less favourably( All this was false allegations) This Senior Manager is a friend to these people, she is the one who openly favours them. They have made reports of minor and false issues against me in the past. They appear to have been influenced by the senior manager to rally against me.
I feel they just want to set me to fail in my position as manager. I feel very much insecure at work , these people want to damage my reputation. The HR Manager is aware, she also found the allegation to be false and she advised me to just ignore them. But do i have a real case gainst these subordinates?