Championship leader David Allingham started as he hopes to go on this weekend, as he led points rival Luke Mossey in opening practice.
The SMS/Nicholl Oils BMW rider clocked a best lap of 1min 29.662secs to end the session 0.314secs clear of Mossey.
Third fastest was Kam Dixon, with Ash Barnes fourth – as Ian Hutchinson rounded out the top five aboard the Team RST BMW.
Pirelli National Superstock Championship, FP1:
1. David Allingham (SMS/Nicholl Oils BMW) 1min 29.662s
2. Luke Mossey (Milenco by Padgetts Motorcycles) + 0.314s
3. Kam Dixon (Kam Dixon Racing) +0.747s
4. Ash Barnes (Rapid Honda with Drivelife) +0.816s
5. Ian Hutchinson (Team RST) +1.084s