Points leader Ben Currie clocked the best lap of opening free practice to lead the way from championship rival Rhys Irwin.
Oxford Products Racing Ducati’s Currie topped the timesheets with a best lap of 1min 29.584secs with two minutes of FP1 to go, knocking Irwin down to second place and 0.238secs adrift.
Zac Corderoy, who had led earlier on in the session, was third at the flag, with Luke Stapleford fourth and Richard Cooper – riding the PHR Performance Triumph as a wildcard entry this weekend – was fifth.
In the GP2 class, Joe Collier was flying, leading the way aboard the Kramer as he finished seventh overall. Cameron Fraser was second in class with Luca Allen third.
Quattro Group British Supersport and British GP2 Championships, FP1 result:
1. Ben Currie (Oxford Products Racing Ducati) 1min 29.594s
2. Rhys Irwin (Astro-JJR Suzuki) +0.238s
3. Zak Corderoy (Gearlink Kawasaki) +0.357s
4. Luke Stapleford (Profile Road & Racing Performance) +0.396s
5. Richard Cooper (PHR Performance Triumph) +0.680s