The 26-year-old Movistar pro beat Edmund Bradbury (NFTO) by over three and a half minutes on the 45km course based at the Cadwell Park Motor Racing Circuit. Ryan Perry (SportGrub) placed third.
Dowsett's ride didn't all go to plan, however, as he left the tarmac on a tight corner and was forced to ride a section of grass. The incident did little to faze the 2015 Bayern Rundfahrt winner and he cruised to a comfortable winning margin.
Simmonds (Team Velosport) added to her 2014 national 10- and 50-mile time trial titles in the women's event, beating Molly Weaver (Liv-Plantur) by 1-18, with Dame Sarah Storey (Pearl Izumi Sports Tours International) in third.
Scott Davies (100% ME) had earlier successfully defended his under-23 men's title, beating Owain Doull (Team Wiggins) and Tao Geoghegan Harrt (Axeon).
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Alex Dowsett on his way to winning the British time trial national championships 2015
(Image credit: Andy Jones)
After an early-season collarbone break, Dowsett has recovered fully
(Image credit: Andy Jones)
Alex Dowsett at full speed on the motor racing circuit
(Image credit: Andy Jones)
Job done! Alex Dowsett claims his fourth national TT title
(Image credit: Andy Jones)
Alex Dowsett gives a post-race interview
(Image credit: Andy Jones)
Alex Dowsett in the national champion's jersey
(Image credit: Andy Jones)
Edmund Bradbury claimed a fine second place behind Dowsett
(Image credit: Andy Jones)
Ryan Perry placed third
(Image credit: Andy Jones)
Hayley Simmonds was the quickest rider in the women's event
(Image credit: Andy Jones)
Hayley Simmonds on her way to claiming the British TT title
(Image credit: Andy Jones)
Hayley Simmonds gives interviews after the podium ceremony
(Image credit: Andy Jones)
Scott Davies successfully defended his under-23 men's title
(Image credit: Andy Jones)
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