Great question Derfred, This is something I often comment about to workmates and trainee directors. If your approaching centre line and nothing heard from director you are suppose to start a turn to final. As A pilot you would be well aware of how ugly things can get on base at parallel runway airports. This rule is in place should you or ATC suffer a comms failure at this crucial point of your flight. In 15 years of director I haven’t seen many cases where something has happen to prevent turning an aircraft to final at that point, but in all cases the pilots went through final.
It would be very poor technique from director to take you right up to final for late turn or even take you through without telling you. You would be within your rights and expected to turn to final, especially if you saw another aircraft on the adjacent base. If your really concerned you may end up going through final perhaps a “approaching centreline” followed by a turn if no response from director. A breakdown of sep with the aircraft your following to the same runway is much preferable than one with the aircraft coming at you on opposite base!