Australian rider Josh Brookes had the bit between his teeth in the second free practice session at Oulton Park, which was again hit by inclement weather.
As a result of the conditions, the organisers were forced to revise Friday's practice schedule, with FP2 put back until 3.40pm.
Brookes surged to the top of the times with a lap in 1m 48.494s and remained there until the chequered flag, although WFR Honda's Alex Lowes and Brookes' Tyco Suzuki team-mate Alastair Seeley reduced the one-second lead he had held over the field for much of the session.
Current British Supersport champion Seeley moved into second place with a lap in 1m 49.025s but was demoted to third by Lowes, who broke into the 1m 48s bracket with a time of 1m 48.757s.
Moto Rapido Ducati's Scott Smart was fourth in the wet conditions in the morning session and held station in the afternoon, posting a best time of 1m 49.08s to put himself ahead of Rapid Solicitors Kawasaki's Shane Byrne.
Byrne's team-mate, Stuart Easton, ventured onto the Cheshire circuit to complete a few laps, although he continues to recover from a knee problem following an operation.
Swan Yamaha's Tommy Hill had powered to the top of the leaderboard in the morning practice with his final lap, but the reigning MCE British Superbike champion was unable to make a similar impact later as he dropped down the order to sixth place on his YZF-R1.
James Westmoreland (WFR Honda), Michael Rutter (MSS Bathams Kawasaki) and Samsung Honda's Michael Laverty completed the first nine, with Gary Mason taking tenth on the Pr1mo Bournemouth Kawasaki.
Mason is filling in this weekend for James Hillier, who was ruled out of the triple-header at Oulton Park following a crash at Knockhill last time out.