Jonathan Powell will appear before parliament for the first time amid questions about his role in the collapse of a trial of two Britons accused of spying for China. Keir Starmer’s national security adviser is due to be quizzed by senior parliamentarians at a private hearing of the joint committee on the national security strategy in the coming weeks. Powell’s appearance will mark the end of a year-long standoff between the committee and ministers, who refused for months to make him available for scrutiny before parliament. The prime minister’s spokesperson…