Leonardo MW (formerly Selex ES) has been developing infrared sensors and cameras for over 62 years at two main sites at Southampton and Basildon. Funding mainly from UK MOD has seen the technology progress from single element PbSe sensors to advanced, high definition, HgCdTe cameras, widely deployed in many fields today. However, in the last 10 years the major challenges and research funding has come from projects within the scientific sphere, particularly: astronomy and space. Low photon flux, high resolution spectroscopy and fast frame rates are the motivation to drive the sensitivity of infrared detectors to the single photon level. These detectors make use of almost noiseless avalanche gain in HgCdTe to achieve the sensitivity and speed of response. Metal Organic Vapour Phase Epitaxy, MOVPE, grown on low-cost GaAs substrates, provides the capability for crucial bandgap engineering to suppress breakdown currents and allow high avalanche gain even in very low background conditions. This paper describes the progress so far and provides a glimpse of the future.