They said the 27-year-old, an experienced competitor on the Snaefell circuit with three podium finishes in the electric Zero TT, was killed at Snugborough on the third of four laps of the Superbike TT.
The race was stopped after the accident with Peter Hickman declared the winner, the result decided by positions after the second lap.
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Mathison’s wife confirmed the tragedy on Monday by posting a message on Mathison’s Twitter account. She wrote:
Not something I ever wanted to write but here we go.....Daley, as Daisy says, is now sleeping with the fairies.
"That’s all I can bring myself to say right now. The last image I saw of my husband, was of a man so happy with life and so proud of his racing.”
The TT races around the island off the north-west coast of England have been run since 1907 and rank among the most dangerous in motorsport. Two riders died last year.
Race organisers ACU Events Ltd have also released a statement, paying tribute to the British rider.
“Daley was an experienced competitor and was seeded 19th for today’s race," it read. "He made his Mountain Course debut in the 2013 Manx Grand Prix Newcomers A Race, finishing fifth.
"His TT career included three consecutive podiums in the TT Zero electric bike Race in 2016, 2017 and 2018 including the runner up position in the race last year, representing Nottingham University.
“He also achieved an 11th place finish in last year’s Superstock Race and a pair of 13th place finishes in the 2017 and 2018 Senior TT Races.
“He set his fastest lap of the Mountain Course - 128.054mph - in the 2018 Superstock race which made him the 34th fastest rider of all time. He set the second fastest TT Zero lap ever with lap of 119.294mph in the 2018 race.
“In total he started 19 TT Races with 14 finishes and 3 podiums and won 6 silver and 8 bronze replicas
“ACU Events Ltd wishes to pass on their deepest sympathy to Daley’s wife Natalie, his family and friends.”
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