The #6 Barwell Motorsport Lamborghini Huracán GT3, driven by Liam Griffin and Alexander Sims, set the fastest time across both morning practice sessions, ahead of qualifying starting at 16:10.
Sims set a time of 1:47.733 towards the end of the second practice session, beating the time set by Jonny Adam in the #17 TF Sport Aston Martin Vantage GT3 in the first session of 1:47.909.
Adam, in the #17 TF Sport car, was second quickest in the second session, setting a 1:48.075 with over 33 minutes remaining, a time which looked unbeatable at one stage.
Third quickest was the #33 Barwell Motorsport entry with a 1:48.189 set by Phil Keen.
The session had a delayed start after the #6 PFL Motorsport Aston Martin Vantage GT3 lost a wheel on its out lap with Pete Littler at the wheel. The team worked hard to get the car back out with six minutes remaining in the session.
In GT4 Aston Martin took two positions out of the top three. The #44 Generation AMR Racing Aston Martin Vantage GT4 set the quickest time with a 1:58.528, closely followed by the #59 Black Bull Ecurie Ecosse McLaren 570S GT4 with a 1:58.717.
The #42 Generation AMR MacMillan Racing Aston Martin Vantage T4 completed the top three on the GT4 time sheets with a 1:58.748.
Qualifying for rounds seven and eight of the British GT Championship starts at 16:10 and follows the usual 10 minute sessions each of the GT3 and GT4 Pro and Am categories of drivers.