Ben Currie took early control at Oulton Park as he powered to the fastest lap in opening practice.
The points leader clocked a best lap of 1min 39.283secs aboard the Oxford Products Racing Ducati with just over a minute until the chequered flag, knocking fellow Aussie Tom Toparis down to second, 0.139secs adrift.
Zak Corderoy emerged third quickest, with Eugene McManus third as Currie’s main title rival Rhys Irwin rounded out the top five.
In GP2, Cameron Fraser was fastest, ending the session 15th overall with Harry Rowlings second and Harvey Claridge third.
Quattro Group British Supersport & British GP2 Championships, FP1 result:
1. Ben Currie (Oxford Products Racing Ducati) 1min 39.283s
2. Tom Toparis (Macadam Racing) +0.139s
3. Zak Corderoy (Gearlink Kawasaki) +0.161s
4. Eugene McManus (Completely Motorbikes Triumph) +0.193s
5. Rhys Irwin (Astro-JJR Suzuki) +0.275s