Luke Stapleford emerged fastest in the opening Supersport free practice session at Thruxton as he saw-off a charge from points leader Ben Currie.
Stapleford banked a hot lap of 1min 18.374secs in the closing minutes, knocking Currie down to second as Jamie Perrin was third.
Perrin ended the session top Suzuki, just ahead of his Astro-JJR team-mate Rhys Irwin as Luke Jones rounded out the top five.
In GP2, Joe Collier was finally back on top as he ended first practice in ninth place overall on the Kramer, with Chassis Factory duo Cameron Fraser and Harvey Claridge second and third, in 18th and 19th positions overall.
Quattro Group British Supersport and British GP2 Championships, FP1 result:
1. Luke Stapleford (Profile Road & Racing Performance) 1min 18.374s
2. Ben Currie (Oxford Products Racing Ducati) +0.019s
3. Jamie Perrin (Astro-JJR Suzuki) +0.054s
4. Rhys Irwin (Astro-JJR Suzuki) +0.371s
5. Luke Jones (Highsparks Ducati) +0.394s