It only benefits Labour most right now because of the current layout of the constituencies. It has benefited the Tories in the past, I believe.
I've just gone over every election since 1900. The 1951 election was the last time the Tories benefited in any way from the electoral system. If you exclude the 1951 election, the Tories hadn't benefited from this system in at least the entire 20th century.