Why did british condemn it as an unlawful assembly and a den of traitors?
What is "it?"
To understand why the British condemned "it" as an unlawful assembly and a den of traitors, I would first need to know more about the specific event or context you are referring to. However, in general, the British might have used such terms to delegitimize a group or organization that they viewed as a threat to their authority and control.
If you provide more information, I can provide a more accurate analysis and explanation.