Toyota driver Gamble tops truncated FP2 at Donington Park
With rain hitting the circuit midway through the 35-minute FP2 session, Gamble ended final practice with the quickest lap after setting a 1'34.836s lap when the conditions were at their best.
Following the brief rain shower, the remainder of the session took place with the field running the wet tyre in the greasy conditions until a late red-flag, triggered by an off-track excursion from Team HARD's Daryl DeLeon, curtailed much of the final running.
Team BMW's Adam Morgan ended FP2 second fastest behind Gamble's Toyota, while Dan Rowbottom upheld honours for the NAPA Racing UK Ford squad with the third quickest time.
Morgan's Team BMW team mate's Stephen Jelley and Colin Turkington finalised their practice running with the fourth and fifth fastest times ahead of Power Maxed Racing Vauxhall's Aron Taylor-Smith in sixth.
Laser Tools Racing with MB Motorsport's Jake Hill ensured all four BMWs ended the session in the top-seven order after producing the seventh fastest time.
Dan Lloyd, Andrew Watson and Michael Crees completed the remainder of the top-ten FP2 order in eighth, ninth and tenth.
Elsewhere, championship leader Ash Sutton and defending champion Tom Ingram were notable absentees from the top placings with the conditions confining the current top-two points drivers to 18th and 20th.