The Shaftesbury trademark is the brand name of a UK importer. Shaftesbury instruments were generally medium to good quality versions of American designs. The Shaftesbury line featured both solid and semi-hollowbody guitars and basses. To hazard a guess, I would assume that the Italian production was featured early on in the late 1960s; as costs rose the importer chose to bring in Japanese-built guitars sometime around the mid-to-late 1970s. As luthier Peter Cook was busy during the 1970s mass-producing decent quality guitars under the Ned Callan, Simms-Watts, and CMI brand names the 1970s would be a good "guess-timate" for the introduction of Ned Callan/Shaftesbury model instruments (source: Tony Bacon and Paul Day, The Guru´s Guitar Guide).
See also Ned Callan. Instruments previously manufactured in Italy and Japan from the late 1960s to the early 1980s. One English-built model was produced during the overall time period.