Alonso, winner at Silverstone last year, had led from pole position but was powerless to prevent Webber powering past six laps from the end and then take the chequered flag with a three second lead.
The victory was the 35-year-old's second of the season, after Monaco, and left him with 116 points to Alonso's 129 after nine of 20 races.
Image: Australia's Red Bull Formula 1 driver Mark Webber, celebrates after winning the Formula One British Grand Prix at the Silverstone circuit, Silverstone, England, Sunday, July 8, 2012. Spain's Ferrari Formula 1 driver Fernando Alonso finished second and Germany's Red Bull Formula 1 driver Sebastian Vettel, finished third.
Text: Reuters Images: AP