Dagley learned to play billiards from two brothers who were good amateur players, Reg and Jack Wright, in his home village of Earl Shilton.

He served in the Korean War whilst on National Service, and once spent a night in a group on a dinghy after the American transport plane that they were on had to ditch.

[2] He was runner-up in the English Amateur Billiards championship in 1963, and from 1964 won the title fifteen times in twenty-one attempts, never again losing in the final.

[4] Dagley won the IBSF World Billiards Championship in 1971, defeating Mannie Francisco in the final, and again in 1975, with Michael Ferreira as runner-up.

[7] In 1987, he defeated Robert Close 3–0, Ian Williamson 3–1, and Mark Wildman 3–0 to set up a rematch of the previous years final against Foldvari.

It was held there as part of the celebrations to mark the bicentenary of the death of the composer Mozart, who was a keen player of billiards.