Formula One race director Charlie Whiting has claimed that Romain Grosjean's decision to ignore the blue flags and not allow Lewis Hamilton to pass during the Singapore Grand Prix was "one of the worst" incidents of conduct he has witnessed in relation to the flag.
Hamilton extended his lead in the driver's championship to 40 points following a victory at the Marina Bay Street Circuit on Sunday, but came through moments of uncertainty during the midway point of the race when he was forced to slow down as Sergey Sirotkin and Romain Grosjean held up the track due to a lack of pace.
Grosjean, in particular, has been accused of simply ignoring the blue flags which are meant to see drivers move to the side to allow faster cars, in this case Hamilton's, to pass by.
"I think Romain forgot the golden rule of blue flags and that's if, you are in a battle, you've got to forget about your own battle and move over," Whiting told the media following the race.
"I've drilled that into them many, many times and he completely forgot about it. The light panels were flashing with his race number on and Lewis was much, much faster.
"It was one of the worst cases of ignoring blue flags that I've seen for a long time."
However, Grosjean was defended by an unlikely ally in Hamilton, who admitted that the flags can be hard to spot.
"It definitely got a little bit interesting towards the end with some of the backmarkers as you already felt the draft from the cars when you were five or six seconds behind, the car would start to slide a little bit more," Hamilton said.
"And you can't really see the blue flags, they are very dark blue, and there are the smallest holes out there [in the fences] so you actually can't really see them until the light panels come on and even when they came on a lot of drivers weren't really responding.
"Max had an opportunity really. I had to go on a massive defence and even then I was still racing the backmarkers, they still weren't lifting off as I was alongside them.
"The hairs were standing up for a second, but then back to business."