Maris Pipers will create the fluffiest and creamiest mashed spuds. You can identify them by their distinct golden-colored skin, creamy white flesh, and starchy consistency.
A key factor in making mashed potatoes is starch content. Ideally, you want to use potatoes that have a high or medium starch content to create a fluffy texture.
Starchy potatoes are easier to mash because of their floury nature. Also note that the higher the starch content in the potatoes, the more water the spuds absorb.
It's clear why Maris Pipers win the prize for the best British potato variety for making mashed potatoes, since their high starch level makes the smoothest and fluffiest mash.