Calum Beach was among a number of riders to clock their best lap of FP1 after the flag as he led the way with a 1min 41.508sec lap to beat Lennon Docherty by 0.169s.
Ted Wilkinson ended the session third after taking a turn at the top of the timesheets after the flag, with Finn Smart-Weeden fourth and Lewis Jones fifth.
HEL Performance British Junior Supersport Championship with Motocourse, Free practice result:
1. Calum Beach (UPVC Outlet Racing) 1min 41.508s
2. Lennon Docherty (Symcirrus Motorsport) +0.169s
3. Ted Wilkinson (Team RMB) +0.199s
4. Finn Smart-Weeden (Wrapped Racing by Club 74) +0.251s
5. Lewis Jones (Symcirrus Racing) +0.339s