A new method is proposed for the determination of the intensity/energy response function of a hemispherical electrostatic analyser as commonly used in photoemission spectroscopy. It only requires the measurement of a wide spectrum of a reference metallic sample. Based only on the knowledge of the Tougaard inelastic electron scattering cross section and an educated parametrization of the response function, the retrieval algorithm minimizes the area of the background subtracted primary spectrum with some constraints. Sound results for different metals (Ag, Au, Cu, Zn) are obtained (i) on two different photoemission instruments (ii) in both fixed analyser transmission and fixed retarding ratio modes (iii) for various lens and slits settings (iv) for both monochromated and unmonochromated x-ray sources. The linear correlation between core level areas and the product of tabulated inelastic mean free paths and of photo-ionisation cross sections validates the approach.