The German, who began in pole position in his BMW 318i, had to chase the fast-starting Alfa Romeo of Gabriele Tarquini, the series leader, for the first eight laps of the shortened 12-lap race, overcoming the Italian with a daring manoeuvre at Becketts.
Tarquini, though, repassed Winkelhock at the next corner before the BMW driver moved ahead for good at Club. Tarquini had slipped to two seconds adrift by the chequered flag.
The race was shortened when a collision between the Renault of Alain Menu and the Toyota of Julian Bailey eventually involved nine of the pursuing pack.
Although Menu continued, those missing from the second grid included all three members of the Nissan team and the field was further reduced when the BMW of Roberto Ravaglia and Giampiero Simoni's Alfa failed at the restart.
Behind the leaders, the New Zealander Paul Radisich won the battle for third place after a long duel with the Renaults of Tim Harvey and Menu and the Peugeot of Patrick Watts. BMW's opening win of the year lifts Winkelhock to eighth overall in the series, but he still has a long way to go to catch the runaway Tarquini.
AUTO TRADER RAC BRITISH TOURING CAR CHAMPIONSHIP: Round 12 (Silverstone, 12 laps, 37.70m): 1 J Winkelhock (Ger, BMW 318i) 24m 40.26s (91.69mph); 2 G Tarquini (It, Alfa Romeo 155) +1.96; 3 P Radisich (NZ, Ford Mondeo) +8.05; 4 T Harvey (GB, Renault Laguna) +12.26; 5 A Menu (Cz, Renault Laguna) +13.68; 6 P Watts (GB, Peugeot 405) +15.20. Fastest lap: Tarquini 2:01.76s (92.89mph, rcd). Total Cup Privateers winner: J Thompson (GB, Peugeot 405). Championship positions: 1 Tarquini 198pts; 2 Radisich 144; 3 J Cleland (GB, Vauxhall Cavalier) 132; 4 Menu 94; 5 Watts 85; 6 G Simoni (It, Alfa Romeo) 66. Manufacturers: 1 Alfa Romeo 198; 2 Ford 169; 3 Vauxhall 160; 4 Peugeot 120; 5 Renault 107; 6 BMW, 100. Total Cup privateers: 1 J Kaye (GB, Toyota Carina) 204; 2= C Goodwin (GB, Vauxhall Cavalier), N Smith (GB, Vauxhall Cavalier) 174.Reuse content