Rosberg crossed the line behind Hamilton, but was deemed to have been in breach of the sport's strict radio rules after he sought advice for a gearbox problem in the closing stages of the race.
Things may get even better for Hamilton, as Rosberg is now under investigation from race stewards, after engaging in radio messages with his team following a gearbox glitch towards the end of the race.
"The Team accepts the Stewards' interpretation of the regulation, their decision and the associated penalty".
A faultless Hamilton led every lap of the race as he claimed his third successive victory at Silverstone and the fourth of his F1 career.
Lewis Hamilton bested Nico Rosberg, and Daniel Ricciardo was again hampered by bad luck as Max Verstappen had the day's standout drive. While Rosberg was pursuing Hamilton, he received a message via the team radio informing him that he'd lost seventh gear.
Hamilton's fourth win of the season was also his third in succession at Silverstone, and the Englishman admitted struggling to absorb equalling Mansell as the most successful home driver at this track.
Rosberg had finished the race, won by Hamilton for the third year in a row, 1.3 seconds ahead of Red Bull's Dutch teenager Max Verstappen.
Nico Rosberg's second place at the British Grand Prix is being investigated for a potential breach of F1's radio regulations at Silverstone.
The rules bar teams from giving drivers assistance during the race, except in certain circumstances.
Sahara Force India relished a double points finish at the home British Grand Prix with Sergio Perez finishing a creditable sixth, just ahead of teammate Nico Hulkenberg. The race stewards claimed that since the new regulations state that the driver must drive the auto alone and unaided, Mercedes' aforementioned instruction was a breach of the Art. 27.1 of the Sporting Regulations. And in eighth was Toro Rosso's Carlos Sainz.
With the penalty and subsequent demotion and loss of points, Hamilton trails Rosberg by just one point in the drivers standings, 168-167.
Rosberg, who had a stirring battle with Verstappen that involved each overtaking the other, said he was confident the team had acted within the rules.