An engine fuel control system for a gas turbine including: a main pump configured to receive fuel from a low pressure source and deliver the fuel at a first high pressure to a supply line; a variable displacement augmenter pump configured to receive fuel from the low pressure source and deliver the fuel at a second high pressure (HPa), when installed in the gas turbine, to one or more fuel pressure operated auxiliary engine devices; and a start valve which is configured to be actuated at low engine speeds to open a flow path which diverts fuel delivered by the variable displacement augmenter pump away from the auxiliary engine devices to the supply line to augment the fuel delivered thereto by the main pump, the start valve being configured to be actuated at higher engine speeds to shut the flow path; characterised in that the main pump is a fixed displacement pump, the variable displacement augmenter pump has a servo-controller to vary its pump flow rate, the fuel delivery flow rate of the variable displacement augmenter pump is variable to compensate for fuel flow demands imposed by the auxiliary engine devices, and in that the engine fuel control system further includes: a fuel metering valve operable to control the flow of fuel between the supply line and a delivery line which, when installed in the gas turbine, delivers fuel to burners of the engine; and a pressure drop control valve which senses a pressure differential across the variable displacement augmenter pump, the pressure drop control valve being arranged to control the servo-controller such that the pump flow rate of the variable displacement augmenter pump is varied to maintain the variable displacement augmenter pump pressure differential at a predetermined level, and being configured to spill, at the higher engine speeds, a portion of the fuel delivered by the variable displacement augmenter pump away from the auxiliary engine devices to the supply line to augment the fuel delivered thereto by the main pump. a main pump configured to receive fuel from a low pressure source and deliver the fuel at a first high pressure to a supply line; a variable displacement augmenter pump configured to receive fuel from the low pressure source and deliver the fuel at a second high pressure (HPa), when installed in the gas turbine, to one or more fuel pressure operated auxiliary engine devices; and a start valve which is configured to be actuated at low engine speeds to open a flow path which diverts fuel delivered by the variable displacement augmenter pump away from the auxiliary engine devices to the supply line to augment the fuel delivered thereto by the main pump, the start valve being configured to be actuated at higher engine speeds to shut the flow path; characterised in that the main pump is a fixed displacement pump, the variable displacement augmenter pump has a servo-controller to vary its pump flow rate, the fuel delivery flow rate of the variable displacement augmenter pump is variable to compensate for fuel flow demands imposed by the auxiliary engine devices, and in that the engine fuel control system further includes: a fuel metering valve operable to control the flow of fuel between the supply line and a delivery line which, when installed in the gas turbine, delivers fuel to burners of the engine; and a pressure drop control valve which senses a pressure differential across the variable displacement augmenter pump, the pressure drop control valve being arranged to control the servo-controller such that the pump flow rate of the variable displacement augmenter pump is varied to maintain the variable displacement augmenter pump pressure differential at a predetermined level, and being configured to spill, at the higher engine speeds, a portion of the fuel delivered by the variable displacement augmenter pump away from the auxiliary engine devices to the supply line to augment the fuel delivered thereto by the main pump. a fuel metering valve operable to control the flow of fuel between the supply line and a delivery line which, when installed in the gas turbine, delivers fuel to burners of the engine; and a pressure drop control valve which senses a pressure differential across the variable displacement augmenter pump, the pressure drop control valve being arranged to control the servo-controller such that the pump flow rate of the variable displacement augmenter pump is varied to maintain the variable displacement augmenter pump pressure differential at a predetermined level, and being configured to spill, at the higher engine speeds, a portion of the fuel delivered by the variable displacement augmenter pump away from the auxiliary engine devices to the supply line to augment the fuel delivered thereto by the main pump.