A fuel system, comprising: a fuel supply; a fuel supply conduit fluidly connecting the fuel supply to an engine; a mechanical fuel pump in fluid communication with the fuel supply conduit; a bypass conduit external to the mechanical fuel pump including a first end fluidly connected to the fuel supply conduit upstream of and proximate to an inlet of the mechanical the fuel pump, and a second end fluidly connected to the fuel supply conduit downstream of and proximate an outlet of the mechanical fuel pump; a bypass valve located on the bypass conduit, the bypass valve configured to allow fuel to flow only from the first end to the second end of the bypass conduit; characterised in that said fuel system further comprises: a relief conduit external to the mechanical fuel pump including a first end fluidly connected to the fuel supply conduit downstream of and proximate to the outlet of the mechanical fuel pump, and a second end fluidly connected to the fuel supply conduit upstream of and proximate to the inlet of the mechanical fuel pump; a normally closed relief valve located on the relief conduit, the relief valve having an open configuration for allowing fuel to flow only from the first end to the second end of the relief conduit; and an electric fuel pump, in fluid communication with the fuel supply conduit, upstream of the mechanical fuel pump and downstream of the fuel supply, wherein the fuel supply, the electric fuel pump and the mechanical fuel pump are fluidly connected in series, and wherein the mechanical fuel pump, the bypass valve, and the relief valve are fluidly connected in parallel. a fuel supply; a fuel supply conduit fluidly connecting the fuel supply to an engine; a mechanical fuel pump in fluid communication with the fuel supply conduit; a bypass conduit external to the mechanical fuel pump including a first end fluidly connected to the fuel supply conduit upstream of and proximate to an inlet of the mechanical the fuel pump, and a second end fluidly connected to the fuel supply conduit downstream of and proximate an outlet of the mechanical fuel pump; a bypass valve located on the bypass conduit, the bypass valve configured to allow fuel to flow only from the first end to the second end of the bypass conduit; characterised in that said fuel system further comprises: a relief conduit external to the mechanical fuel pump including a first end fluidly connected to the fuel supply conduit downstream of and proximate to the outlet of the mechanical fuel pump, and a second end fluidly connected to the fuel supply conduit upstream of and proximate to the inlet of the mechanical fuel pump; a normally closed relief valve located on the relief conduit, the relief valve having an open configuration for allowing fuel to flow only from the first end to the second end of the relief conduit; and an electric fuel pump, in fluid communication with the fuel supply conduit, upstream of the mechanical fuel pump and downstream of the fuel supply, wherein the fuel supply, the electric fuel pump and the mechanical fuel pump are fluidly connected in series, and wherein the mechanical fuel pump, the bypass valve, and the relief valve are fluidly connected in parallel. a relief conduit external to the mechanical fuel pump including a first end fluidly connected to the fuel supply conduit downstream of and proximate to the outlet of the mechanical fuel pump, and a second end fluidly connected to the fuel supply conduit upstream of and proximate to the inlet of the mechanical fuel pump; a normally closed relief valve located on the relief conduit, the relief valve having an open configuration for allowing fuel to flow only from the first end to the second end of the relief conduit; and an electric fuel pump, in fluid communication with the fuel supply conduit, upstream of the mechanical fuel pump and downstream of the fuel supply, wherein the fuel supply, the electric fuel pump and the mechanical fuel pump are fluidly connected in series, and wherein the mechanical fuel pump, the bypass valve, and the relief valve are fluidly connected in parallel.