By Charlie Conchie London’s listed firms have been dusting off “defence manuals” and conducting “dry-runs” in recent months as they prepare to fend off unwanted approaches from private equity houses, insiders have toldCity A.M. City lawyers and PR firms say they have been drafted in to prepare defensive efforts for London-listed companies ahead of a predicted wave of takeover attempts from private buyers in the coming months. Lawyers at law firm Herbert Smith Freehills said a number of potential buyers were “poised” for deals in the opening months of the year, and target companies had been for…