Even in Britain, where impeachment extended beyond removal of public officers but also to charge private citizens for crimes not prosecuted by the Crown, and thus more closely resembled a criminal prosecution, ...
... the rights now embodied in our sixth amendment did not apply in the charging phase before the House of Commons.
Here’s what the leading British parliamentary procedure treatise said in the 19th century about the procedure in the House of Commons in impeachments: 
Only when the impeachment were tried in the House of Lords, did the accused have the right to defend himself with witnesses and the assistance of counsel:
That was precisely the approach adopted by the framers of the United States Constitution when they provided for impeachment of federal officers by the House of Representatives and impeachment trials in the Senate.
*impeachments
