Presented is a proposed search for ultra light dark matter with the Atomic Interferometric Observatory and Network (AION)- a UK led initiative to design and build a multipurpose atom interferometer with the goal of probing the properties of dark matter and paving the way to detecting gravitational waves in the largely unexplored mid-band frequency range. The plan is to build a set of atom interferometers with progressively larger baselines, taking advantage of the design features used by the world's best atomic clocks in combination with established techniques for building inertial sensors. The key experimental features of the interferometer and the type of dark matter models that can be probed is presented.