I've been in a legal battle with a customer for the last 8 months trying to get what I'm owed for the delivery services we provided for his company. Recently I got in touch to say that if he wanted to settle before court then it would be a good time to make an offer because we're getting too close to the court date to turn back now. The resulting barrage of emails flying back and forth were horrendous. The guy had clearly lost his cool and was just aggressively spouting all kinds of abuse back at me. Most of it washed off me no problem but in one of his last emails he suddenly blurted out "I know you have mental health issues" (which I don't) and then stated "I suggest you seriously consider the offer because you don’t want H&S, immigration and insurance companies knocking on your door." I'm intending to use this in court against him, but my questions is:- could this be considered more serious? Is it a threat or even blackmail?