Billy McConnell beat Joe Francis to the fastest time in the opening session at Oulton Park, clocking a 1m:36.396 lap of the Cheshire track.
Alex Olsen ended the session third and just over half a second adrift of McConnell, as David Allingham finished fourth, just ahead of Davey Todd.
Pirelli National Superstock Championship with MotoNovo Finance, Oulton Park, free practice one:
1. Billy McConnell (C&L Fairburn Properties/Jackson Racing)
2. Joe Francis (Stauff Fluid Power Kawasaki) +0.562s
3. Alex Olsen (FHO Racing with Kobelco) +0.574s
4. David Allingham (TAG Racing Honda) +0.613s
5. Davey Todd (Milenco by Padgetts Motorcycles) +0.921s