Galaxy Surveys are a key resource for observational cosmology, with the potential to provide the answers to many fundamental questions in modern physics. The Darksurvey project will use the Dark Energy Survey (DES) and extended-Baryon Oscillation Spectroscopic Survey (eBOSS) within which Will Percival has key leadership positions, and future projects including MS-DESI to measure the cosmological expansion rate between redshifts 0.5 and 2, testing Dark Energy. Complimentary structure growth measurements will test Einstein's theory of Gravity on the largest scales possible. The large-scale clustering of galaxies will be used to constrain primordial non-Gaussianity, testing and constraining models of inflation. The scale-dependence of the clustering signal will be used to measure the masses of neutrinos through their early Universe effects, and to set constraints on the evolution of galaxies and structure over cosmological time-scales. Parallel development of innovative tests and measurement methods will be undertaken to enable and enhance these results, while joint analysis with CMB and weak-lensing data will be used to perform additional tests, and to break degeneracies present when cosmological models are tested.This grant will consolidate the world-leading position of the group initiated by Will Percival at the University of Portsmouth, and developed over the last 4 years. Furthermore, it will train and develop a group of scientists within Europe with the key experimental skills required for the ESA Euclid mission.