The joint driver standings leader set a 2m05.673s to take the top spot, closely followed by Abbi Pulling, less than 0.2s behind her.
Chadwick, driving for Veloce Racing, also led first practice, while Pulling also finished second in the earlier session for the PUMA team in just her third race weekend in the series.
2019 runner-up Beitske Visser (M Forbes Motorsport) came third, as she did in the earlier session, with PUMA’s Marta Garcia in fourth and title contender Alice Powell in fifth for Racing X.
The session was red-flagged after Abbie Eaton (Ecurie W) span in Sector 1 with seven minutes of running remaining and was unable to restart her engine, leaving her stranded in the middle of the track.
Chadwick and Powell head into the season finale joint on 109 points, with the latter leading with three wins, having won last time out at Zandvoort, to Chadwick’s two.
Chadwick was top of the timesheet 10 minutes into the session, with a 2m06.750s putting her almost half a second clear of her second-placed team-mate Bruna Tomaselli.
Caitlin Wood, Alice Powell
Photo by: Mark Sutton / Motorsport Images
Jessica Hawkins (Racing X) moved up into second at the halfway mark, setting a 2m07.085s to split the two Veloce-sponsored cars.
Returning to the track for the second stint, Bunker Racing’s Sabre Cook took the second-quickest spot at her home race, just 0.1s off Chadwick’s time.
Visser pipped Chadwick to the top spot with 10 minutes to go, setting a 2m06.619s before bettering her own time by 0.2s, but Chadwick reclaimed the lead seconds later, going 0.5s clear.
This is the first weekend to see two W Series races, with the drivers’ best times in qualifying setting the grid for the first race, on Saturday evening, while their second-best time will determine the starting grid for race two on Sunday.