Louis Valleley beat Max Cook to day one bragging rights as he clocked the only sub 1:18 lap of the session with a 1m 18.91s lap.
Cook was 0.396secs adrift, with Aaron Silvester third, Franco Bourne fourth and Edmund Best finishing the day fifth.
Pirelli National Junior Superstock Championship with MotoNovo, Thruxton, combined practice.
1. Louis Valleley (Team Val-Tech Racing/Mortimer Racing) 1m 18.821s
2. Max Cook (Uggly & Co by Binch Pro) +0.396s
3. Aaron Silvester (A&J Racing) +0.532
4. Franco Bourne (Marvel HCL Motorsport) +0.619s
5. Edmund Best (Symcirrus Motorsport) +0.655s