NOVELTY - The turbine has blades (23,24) which are formed around an axis where the blade is on pivot mountings close to the feet, hydraulic pump (52) and a generator (53). An effective swept area of the turbine blades is adjustable an actuator (29) i.e. hydraulic ram (27) connected to blades. The movement of actuator turning the blades on the pivots are configured to align blades more closely to the axis/to move the blades away from the axis and a control valve (43) controls hydraulic pressure in the actuator responsive to pressure of a hydraulic fluid pumped by the hydraulic pump.    USE - Tidal flow power generation turbine/coning turbine for energy generation.    ADVANTAGE - The position of the turbine blades are allowed to be varied in a variable conical relationship depending upon the requirements of the generator and in particular to prevent over-rotation of the generator. Pressure in the hydraulic ram is reduced as the hydraulic fluid is vented from the hydraulic ram responsive to excess pressure in the hydraulic fluid pumped to the generator. As the configuration of the blades in operation are varied between the maximum expanded and maximum contracted configuration dependent upon the tidal flow rate and/or power output requirement of the turbine, a more expanded blade configuration is adopted to accommodate relatively lower tidal flow speeds and a relatively more contracted configuration is adopted at relatively higher tidal flow speeds. Hence higher power output is provided for a given tidal flow speed in the more expanded blade configuration and a lower power output is provided for a given tidal flow speed in a more contracted configuration. The relatively more contracted configuration protects against damage to the turbine at times of high tidal flow speed. An effective and efficient harnessing of tidal flow power at low flow rates is enabled and the system is ensured that is not structurally compromised when exposed to high flow rates.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross sectional view of a tidal flow turbine system through an actuator control system.    Turbine blades (23,24)    Hydraulic ram (27)    Actuator (29)    Control valve (43)    Hydraulic pump (52)    Generator (53)