Update...
Moving the servo to a different pin cured the bounce problem.
I've been using a Mega 2560 up until now but I've just written the code to a Pro Mini and noticed something very strange.
When I use:
int minPulse = 1000;
int maxPulse = 2000;
on the Pro Mini to control the servo limits, the servo only travels a fraction of the distance it did when connected to the Mega 2560.
I thought the limits were 550 and 2500, and that it would be the same no matter which flavour of Arduino the code was running on but in order to achieve the degree of servo movement I need, I've had to replace 1000 and 2000 with 1500 and 4000 respectively... does anyone know why this might be?