Luke Stapleford remained in control to take the best time of the day across the combined free practice times.
After clocking the fastest lap in FP1, he shaved a huge chunk off his earlier time as he banged in a 1min 30.422sec lap to go 0.539secs clear of reigning champ Ben Currie.
Jack Kennedy was third, as new arrival Can Oncu powered up to fourth in just his second session in the series, as Rhys Irwin rounded out the top five.
In GP2, Jack Nixon stayed at the top, just ahead of his Kramer Racing team-mate Owen Jenner, with Luca Allen third.
In the Cup, Cameron Hall led Tom Tunstall, with Adon Davie third.
Quattro Group British Supersport, GP2 and HEL Supersport Cup, combined practice:
1. Luke Stapleford (Macadam Triumph Racing) 1min 30.422s
2.Ben Currie (Oxford Products Racing Ducati) + 0.539s
3.Jack Kennedy (Honda Racing UK) +0.795s
4.Can Oncu (Gearlink Kawasaki) +0.813s
5.Rhys Irwin (Astro-JJR Suzuki) +0.884s