Control of a fuel supply system

A fuel control system for a combustion engine, the system being characterised by comprising: an electrically driven centrifugal pump (220; 429; 620) operable at a pump speed, wherein the pump is arranged to supply pressurised fuel to the engine, and a pressure raising valve (224; 424; 524; 624) for ensuring the pressure of fuel within the fuel control system is maintained above a predetermined, minimum amount, wherein the pressure raising valve is adapted to provide a substantially linear variation of fuel flow rate to the engine with pump speed. There is also disclosed a pressure raising valve for use in such a system.