We present the Lancaster Astrophysics Metal Poor Star Search (LAMPSS) in the Milky Way halo, conducted using the metallicity-sensitive Ca H & K lines. We use the CaHK filter of the MegaPrime/MegaCam on the Canada-France-Hawaii Telescope (CFHT) to survey an area of 1.010deg2 over the COSMOS field. We combine our new CaHK data with broadband optical and near-infrared photometry of COSMOS to recover stars down to mHK ∼ 26. After removing galaxies, we find 70% completion and 30% contamination for our remaining 1772 stars. By exploring a range of spectral types and metallicities, we derive metallicity-sensitive colour-colour diagrams which we use to isolate different spectral types and metallicities (−5 ≤ [Fe/H ≤ 0). From these, we identify 16 potentially extremely metal-poor stars. One of which, LAMPS 1229, we predict to have [Fe/H] ∼ −5.0 at a distance of (78.21 ± 9.37) kpc. We construct a Metallicity Distribution Function for our sample of metal-poor stars, finding an expected sharp decrease in count as [Fe/H] decreases
