Matt Truelove saw-off a charging Luke Mossey to lead the opening Superstock session by 0.226secs.
The TAG Racing Honda rider set the pace with a hot lap of 1min 16.527secs as Mossey ended FP1 in P2 with Lewis Rollo third.
Simon Reid emerged fourth fastest at the flag with Josh Owens fifth.
Pirelli National Superstock Championship, FP1 result:
1. Matt Truelove (TAG Racing Honda) 1min 16.527s
2. Luke Mossey (Milenco by Padgetts Motorcycles) +0.226s
3. Lewis Rollo (Motorrad Central Edinburgh by MLav Racing) +0.935s
4. Simon Reid (Carl Cox BMW by MLav Racing) +0.987s
5. Josh Owens (SAF Holland Honda) +1.018s