I wouldn't say it lost its effect. There were still strategic items such as Tungsten and other additive metals that were in very limited or negligable supply that severely effected the quality and or quantity of weapons produced. Stockpiling helped but still required the rationing of material which affected production of engines, armor, armorpiercing ammunition and other items.
There was one positive outcome of the blockade. When the Coca-Cola organization was cutoff from the base syrup needed to produce their signature product they went to work and developed an artificially flavored soft drink that used readily available beet sugar instead of cane sugar and artificial flavoring (and color) that could be locally produced. That product (Orange Fanta) proved popular and was even adopted by the parent company after the war.
That wasn't the result of the blockade, but of the economic warfare program that had the Allies try to buy up tungsten from neutrals, something that was more effective after the US entered the war and added it's wealth to the program, which IMHO means it wasn't the effectiveness of the British blockade as much as US economic warfare.
The other part of it was Norway was a huge source of critical minerals, which until about 1943 was basically uninterrupted, but at that point the RAF did bomb some crucial mines, which then deprived Germany of their biggest sources of specific minerals and caused the shortages. So not the blockade after conquering Europe, but rather more direct economic warfare.