Tom Booth-Amos ended day one on top after beating Jaimie van Sikkelerus to the best time of the day.
The Gearlink Kawasaki rider’s lap of 56.546secs in second practice was enough to power him to the top of the timesheets, beating van Sikkelerus by 0.159s.
Ashcourt Racing's Lee Johnston – who had led the morning session – was third quickest, just ahead of Rhys Irwin as Tom Toparis rounded out the top five.
In GP2, Cameron Fraser led the charge in 13th spot overall, closely followed by Joe Collier with Harry Rowlings third.
Quattro Group British Supersport/GP2: Combined practice
1. Tom Booth-Amos (Gearlink Kawasaki) 55.529s
2. Jaimie van Sikkelerus (MPM Routz Racing Team) +0.159s
3. Lee Johnston (Ashcourt Racing) +0.159s
4. Rhys Irwin (Astro JJR Suzuki) +0.242s
5. Tom Toparis (Macadam Racing) +0.277s