The Peugeot 107 driver has been the pacesetter for much of the series' season so far, although he narrowly missed out on completing a hat-trick in the reversed-grid finale.
Nevertheless, Lettis leaves Kent with 11 wins to his name - five behind long-time table-topper Freddie Slater - and leaps up four places on the leaderboard to eighth.
Lettis is the only change inside the top 10 of Autosport's table this week with the majority of the drivers not in action, although Formula Ford 1600 star Lucas Romanek failed to add to his tally despite there being three different National FF1600 victors at Brands.
Instead, the next highest improver is Toyota MR2 pilot Dan Silvester, who picked up another class win at Silverstone to jump from 17th to 13th, although he was defeated second time around.
One driver who went unbeaten over the weekend, however, was Type R Trophy conqueror Joe Jessup. He won all three Northamptonshire bouts to provisionally seal the title as well as rocket from outside the top 50 and into 19th in the rankings.
Source: Autosport