An apparatus for controlling the flow of downhole fluids comprises a body having a throughbore and at least one port extending through a sidewall of the body to enable fluid communication between the throughbore and an exterior of the body. The apparatus comprises a flow control device for controlling the flow of fluids through the port. The flow control device is arranged to change configuration between a closed configuration in which fluid flow through the port is restricted and an open configuration in which fluid flow through the port is permitted. The apparatus further comprises an actuator mechanism associated with the flow control device for selective actuation of the flow control device to change the configuration of the flow control device between the closed and open configurations. The apparatus further comprises a locking device to lock the configuration of the flow control device, and an unlocking mechanism to unlock the locking device and to permit the actuator mechanism to change the configuration of the flow control device.