Championship leader Aaron Silvester took charge as the action began at Brands Hatch, beating Louis Valleley to top the FP1 timesheets by 0.374secs with a best lap of 1min 30.912s.
Cameron Hall ended the session third, some 0.266secs adrift of Valleley as Sam Laffins was fourth and Taylor Rose rounded out the top five.
Pirelli National Junior Superstock Championship with Santander Consumer Finance, FP1 result:
1. Aaron Silvester (A&J Racing) 1min 30.912s
2. Louis Valleley (LVR) +0.374s
3. Cameron Hall (Triple M powered by Nationwide Electrical) +0.620s
4. Sam Laffins (Uggly & Co by Binch Pro) +0.840s
5. Taylor Rose (TRR27 Verkade Racing) +0.999s