Quote from Kassz007:
The British were certainly not insignificant. German U-Boats would have owned the Atlantic if the British didn't fight them. Not to mention their efforts in Africa.
Hitler decided to invade USSR instead of Britain because they couldn't defeat the RAF and establish air superiority in order to get their troops across.
Until the introduction of the radar, neither British nor later Americans could defeat the U Boats. At the beginning of the war they have sunk so many of the British merchant marine that it was beginning to effect UK.
As for the Africa Korps, Romel was defeated because he could not get supplies and not because the English were better at fighting. Anybody who is familiar with WWII will tell you that. The events in Norway, Greece, and Crete illustrated beyond dispute the superiority of German fighting machine v. the British.
The Germans did not finish off Britain because they decided to defeat the Soviet Union first. They needed their resources (oil especially) to continue fighting. The battle of Dunkirk eliminated 90% of British armor and they were not ready to repel the invasion in 1941. They got their asses kicked in northern France and in Narvik when they tried stopping the German invasion of Norway and that was before the Nazis invaded USSR.