Germany's Auto Motor und Sport has revealed the details of a team bosses meeting that took place at Silverstone on Thursday.
They were told by FIA officials that Alonso and Hamilton technically broke the rules at Valencia, and would have been sanctioned if rival teams lodged official protests.
Hamilton reportedly overtook pole sitter Sebastian Vettel twice on the pre-race warm-up lap; a practice that is not allowed.
And Spaniard Alonso also broke the rules by accepting the Spanish flag from a marshal on the slowing-down lap, after thrilling the partisan crowd by winning.
Meanwhile, Blick newspaper has crowned Hamilton the unofficial "bad guy" of Formula One, on the basis of a document doing the rounds in the Silverstone paddock.
It is a list of all the punished offenses in F1 over the last ten years -- with the 27-year-old British driver in clear pole position.