At the Isle of Man TT, Jefferies was the first rider to lap in excess of 125 miles per hour (201 km/h) and the first to win three races during the week-long festival for three consecutive years.

Jefferies approached the turn on his TAS Racing GSX-R1000, following a lap of 125 mph average speed (the fastest in that practice week).

Jefferies reportedly hit the wall of number 29 Woodlea Villas bordering the turn before he and his machine were hurled back across the circuit, taking lumps of debris across the road and bringing down a telephone pole in the process.

In the aftermath of the crash, fellow rider Jim Moodie did not have enough time to brake when he reached the scene and rode into the telegraph lines which were hanging across the road due to the incident;[3] three of the lines snapped; however, one came over his motorcycle's windscreen and nearly killed him when it wrapped round his throat; it snapped at the last minute and Moodie escaped with his life; however, he retired from TT competition shortly afterwards.

[4] Later that day, the TT organisers released an official statement which read: 'It is with regret that the organizers of the Isle of Man TT races, the Auto-Cycle Union, announce that David Jefferies, of Baildon in West Yorkshire, who crashed on the second lap of this afternoon's practice session, received injuries, which proved fatal.