Miles won the British Chess Championship only once, in 1982. His prime time as a chess player was in the middle of the eighties. In the January 1984 FIDE rating system, he ranked #18 in the world with a rating of 2599. One of his best (and most controversial) results was his win at the Tilburg tournament in 1984. The following year, he tied for first there with Robert Hübner and Viktor Korchnoi, playing several of his games while lying face-down on a table, having injured his back.