The Legend of Zelda: Tears of the Kingdom is the biggest boxed video game launch of the year in the UK.
GfK also reveals that the game is Nintendo's second biggest release in UK history by revenue, behind 2008's Wii Fit. If we discount the Balance Board price, it is actually the biggest Nintendo release by revenue. In terms of units, the game only lags behind Wii Fit and combined sales of Pokémon games (namely: combined sales of Sun and Moon, and Scarlet and Violet).
Its opening week sales eclipse the boxed sales of Hogwarts Legacy by more than 50%. This is just boxed sales, and Hogwarts, which was released on PC, PS5 and Xbox Series S and X in February, did have a very strong digital launch. Switch digital sales are typically much lower than the other platforms, so it's unknown if the game outsold Hogwarts overall (Nintendo doesn't share digital data with the charts companies).