“Leicester are going to win the Premier League!” the photographer calls out from behind the camera. “Smile!” “They’ve not won it yet,” mutters Mark Selby, lips resolutely horizontal, holding aloft his Leicester City scarf in a manner that brings to mind a hostage clutching the morning newspaper in order to show his family he is still alive.

If ever an exchange captured a man, this is it. Selby is the world’s No 1 snooker player returning to the Crucible Theatre in Sheffield, scene of his greatest triumph. He is 32 and in the prime of life: a wife and daughter at home, his boyhood football team about to clinch a most fantastical triumph.

And yet there is a basic glass-half-empty melancholy to the 2014 champion, a rumbling world-weary discontent that only occasionally lifts. He speaks lucidly and politely, but rarely smiles. The purpose of this interview is to find out why.

When others talk about Selby, a portrait quickly emerges: of a player who may not be blessed with outrageous natural talent, but would rather sell a kidney than give you an easy starting red. “A matchplay animal,” Steve Davis says of him. “The most dedicated snooker player I’ve ever seen,” reckons Willie Thorne. Ronnie O’Sullivan, beaten by Selby in the world final two years ago, calls him “The Torturer”: dogged, doughty and horrible to play.