Two riders died after an 11-bike crash during the British Supersport Championship race at Oulton Park on Monday.
Owen Jenner, 21, and Shane Richardson, 29, were fatally injured in a "major chain reaction" incident on the first lap of the race and a third rider Tom Tunstall, 47, sustained "significant injuries".
The race was halted on the first lap after what series director Stuart Higgs later called a "severe and catastrophic" incident as he announced the event was cancelled.
BBC Sport looks at what happened and what is next for the sport.