The Allied campaign in Norway took place from April 1940 until early June 1940. It was in two main parts, in central Norway and around Narvik.
The British campaign was coincidentally commenced simultaneously with Nazi Germany's invasion of Denmark and Norway in Operation Weserübung of April 9.
In central Norway, the campaign was centered on Åndalsnes and Namsos.A fuller description of the battles in the latter can be found at Namsos in April 1940. British bases were established at those two ports very soon after the German invasion. However, in the face of German air superiority, it proved impossible to maintain forces there. After penetrating into the valley of Gudbrandsdalen, British forces were withdrawn from central Norway in early May.
The focus of the campaign then shifted northwards. Around Narvik, greater success was gained by British forces in cooperation with Polish, French and Norwegian troops. In the First and Second Battle of Narvik British naval forces had devastated German naval power in the area, and land forces later captured Narvik itself. Also, unlike central Norway, land-based airpower was established at a reasonable level, and the Luftwaffe did not have undisputed control of the air.
However, eventually, German success in the Low Countries and France with the invasion commenced on May 10 meant that larger concerns overtook the British and French governments, and German forces pressing up towards Narvik by land from central Norway began to threaten the Allied position at Narvik. Allied troops were evacuated from Narvik in Operation Alphabet by June 8, 1940.
The fiasco of the British campaign - with its missed opportunities and squandered victories - might reasonably be said to be the responsibility of Winston Churchill, the British First Lord of the Admiralty. But, in fact, the 'Norway Debate' in the British House of Commons, which saw large numbers of Conservative Party MPs refuse to back the Prime Minister, Neville Chamberlain, led directly to Chamberlain's resignation and Churchill's appointment as Prime Minister on the afternoon of 10 May.