The Norway Debate was never about Norway per se. It was about the dissatisfaction of much of the Commons on the general conduct of the war. People felt that the war wasn't being pressed with the seriousness it needed. Nobody wanted to go after Winston or Pound. It was all about Chamberlain, and the specifics of Norway was simply a chance to articulate criticism towards him.
In defense of Churchill, you can't expect him to be entirely responsible for the fall of Norway. His brief was to initially mine the waters, not prevent a German invasion. The general lack of preparedness to do so did not lie in his arena, but with Chamberlain. Besides, you don't sack one of your best commanders or ministers because of one failure.
Since the Norway Debate didn't even push out Chamberlain (he won the vote of no confidence, but the defection of various backbenchers and signs of unpopularity convinced him to resign on his own), it can hardly pull down Churchill as well.
I am very bothered by Hoist40's suggestion that the German invasion was entirely in response to Britain. Both the Germans and Britains could read a map and knew how important Norway was. As early as October 1939 (way before the Altmark incident) Admiral Raeder drew up plans for invading Norway to use it for naval bases. While this was partially because of concern of British action against the iron ore, it was mainly for offensive reasons against Britain. In December 1939, Hitler met with Vidkun Quisling where they discussed theoretical British threats to Norway, and afterwards asked for invasion plans to be drawn up which were later revised throughout January and early February 1940, all before the Altmark incident. It is incorrect to state that it was only because of British plans to mine or invade that "provoked" Nazi Germany to invade themselves as a reponse. Both countries knew of the strategic importance of Norway, and knew how advantageous it would be if the Germans controlled it. To say that simply because the iron ore passage was blocked by mines excuses German actions is to give them a pass they did not deserve. You can justify any invasion by saying if they didn't, it would hurt the German war effort. Instead, the British plans was based on their correct assumption that Hitler would invade Norway at some point. The idea that the Germans were somehow pushed into it against their will is laughable.