Strange as it may seem, the Dieppe Raid of 1942 may have been the most important thing the British did in the whole war. German intelligence detected the naval build-up for Dieppe, and it was assumed a large naval landing would take place. Hitler was worried and ordered some of his best panzer divisions taken from Russia to France. These divisions remained in France until winter 1942. Had they remained in Russia they might have prevented 6th army from being surrounded. By the time they went back to Russia it was too late.He did the same for Roosevelt who had died some days earlier so he felt obliged to do the same for the Chancellor of Germany.
As for defeating Hitler it was something well beyond the powers of the UK to do alone. Their contribution to final victory while great was dwarfed by that of Russia & the USA.