For clarity: The upper house (the House of Lords) is appointed, rather than elected. The instant runoff voting was used to select which hereditory peers would be allowed to remain sitting in the house after the number of sitting hereditory peers was reduced to 90 in 1999, with the electorate being other members of the house.
UK rejected alternative voting in 2011 for Lower House: https://en.wikipedia.org/wiki/United_Kingdom_Alternative_Vot...
So the winner take all would remain for a while.