He is a member of the UK Dark Matter Collaboration, and Sumner's interests cover a wide range of astronomy-related fields, focusing particularly on particle physics.

He joined the Cosmic-Ray and Space Physics group at Imperial College in 1979, and in 1984 became the project manager for flight hardware for the x-ray satellite ROSAT.

He became involved in the search for the direct demonstration of the existence of galactic dark matter, known as "Weakly Interacting Massive Particles".

[1] New Scientist described him as "leading the search for galactic dark matter, including axions, at Imperial College London in the UK".

He is a Fellow of the Institute of Physics, and of the Royal Astronomical Society, and holds the position of Vice-Chair, COSPAR - Commission H. Scopus lists him as having had 132 peer-reviewed publications and cited in 7000.