Dr Thomas Collett has measured the behaviour of dark energy with a double source-plane gravitational lens, establishing these objects as vital probes of cosmology and he has precisely measured the ‘gravitational slip’, describing how space and time are distorted by gravity. Collett also leads the strong lensing group for the Large Synoptic Survey Telescope’s Dark Energy Science Collaboration. For these reasons, Dr Thomas Collett is awarded the Winton Award.