I infringed. Travelling approx. north south, in receipt of a RIS when asked to change squawk for next unit and wished a safe journey with frequency and "they have your details". Lo and behold unit RT was temporarily very busy so a short delay in getting a word in edgeways and then told I had entered CAS without permission. True no doubt but what would you have done? What was the correct procedure? Orbit in the CAS from which I had been cleared?