Asymmetry across biological membranes is vital for a wide range of organelle and cellular functions. Significant differences in lipid composition have been found between the inner and outer leaflets of bio-membranes, yet the rate of phospholipid flip-flop (movement of a lipid from one leaflet to the other) is currently very difficult to measure and estimates of this cover several orders of magnitude. Critically, lipid modification to incorporate tags (for instance fluorescent groups) is likely to significantly affect flip-flop rates and so it is extremely important to develop chemical-label free methods of detecting asymmetry and measuring flip-flop rates. Here we aim to apply a recently-developed method based on contrast-variation neutron scattering to systematically measure inter-vesicle lipid exchange rates and intra-vesicle flip-flop rates in a number of model vesicle membrane system