Championship leader Luke Stapleford started the weekend as he hopes to go on by powering to the top of the FP1 timesheets.
The Scars-Racing Ducati rider set an early quick lap of 1min 17.201secs which could not be beaten by any of his rivals in the remainder of the 25-minute session.
Dean Harrison emerged fast from the outset, leapfrogging his Honda Racing UK team-mate, five-time champion Jack Kennedy in the closing minutes to go second quickest, 0.240secs adrift of Stapleford.
Kennedy remained third at the flag as Corey Tinker enjoyed his best session of the season so far to finish fourth fastest aboard the Josh Davis Motorsport Ducati as Oliver Barr rounded out the top five.
James Alderson began the weekend fastest in the Cup class ahead of Cam Swain, with Stephen Thomas third.
Quattro Group British Supersport Championship, FP1 result:
1. Luke Stapleford (Scars-Racing Ducati) 1min 17.201s
2. Dean Harrison (Honda Racing UK) +0.240s
3. Jack Kennedy (Honda Racing UK) +0.378s
4. Corey Tinker (Josh Davis Motorsport) +0.907s
5. Oliver Barr (Binch Pro Ducati) +0.960s