Cavendish produced a trademark sprint finish on the uphill Guildford incline outside the capital to rack up his third stage victory of the tour ahead of next Sunday's road race in the Netherlands, where he will defend his world road race title.
Tiernan-Locke, who will join forces with Cavendish and Tour de France winner Bradley Wiggins for the nine-man British team around the Limburg course in a week's time, held on to his overnight lead of 18 seconds.
The first home winner of the Tour of Britain in 19 years was already looking forward to a battle to help Cavendish retain his world title.
"Whatever role I'm given I'm confident I can do a good job. The success of British cyclists has been a real inspiration," Tiernan-Locke told Sky Sports.