THE 23rd Warwick and Leamington Festival from Tuesday July 2, to Sunday, July 14 promises to be as exciting, interesting and remarkable as in previous years. A wide variety of concerts is included in the 13-day programme, including the celebration of the centenary of the birth of Sir William Walton through "Faade," "Belshazzar's Feats," and a dozen other smaller scale works, plus two exhibitions. Festival director Richard Phillips said: "One of our principal strengths is the variety of venues that we use, from the grandeur of Warwick Castle to the historic heritage of buildings in Warwick .