Tom Toparis earned first practice bragging rights as he beat Rhys Irwin to the top spot with a 1min 52.911sec lap.
The Macadam Racing rider displaced early leader Ben Currie with five minutes of the session to run, backing it up with yet another quick lap to seal the deal.
Astro-JJR Suzuki’s Rhys Irwin continues to look strong a week after making his World Supersport debut, ending the session second quickest with Currie third. Ash Barnes finished fourth, just ahead of Luke Stapleford.
Joe Collier was back to his dominant best in GP2, ending top in class and 14th overall, just one place ahead of Cameron Fraser as Harvey Claridge was third.
Quattro Group British Supersport and GP2 Championships, FP1:
1. Tom Toparis (Macadam Racing) 1min 52.911s
2. Rhys Irwin (Astro-JJR Suzuki) +0.142s
3. Ben Currie (Oxford Products Racing Ducati) +0.369s
4. Ash Barnes (Barney Racing) +1.025s
5. Luke Stapleford (Profile Road & Racing Performance) +1.044s