Had a pleastere guy, rescrew loose boards, re plaster, tape and skim walls but cracks re-appearing?

Joints in plaster board often crack due to building movement, changes in temperature, humidity etc, even on new work. From your description it seems your plasterer did a good job. As Gottcha has posted using a flexible filler, often called decorators caulk, on joints and minor cracks usually cures the problem.