Sep.6 (GMM/ Lewis Hamilton’s Monza win has fallen under a dark cloud.

In the closing laps of the Italian grand prix, the Briton was told by his Mercedes engineers to speed up — but they did not tell him why.

“Those last few laps were not cool,” Hamilton said on the victory lap.

And boss Toto Wolff initially told British television Sky immediately after the chequered flag: “It’s still a secret.”

It soon emerged that Jo Bauer, the FIA’s safety delegate, had referred a matter to the stewards about tyre pressure.

With the Pirelli blowout saga still looming large, F1’s tyre supplier had insisted before Monza that teams must increase pressure for Monza.

But on the grid, Pirelli’s Paul Hembery said the teams were “mainly” playing ball with the strict new limits.

It emerges that, with a calibrated tyre gauge, Pirelli had checked the rear tyres of both Mercedes and both Ferraris on the grid — and the pressure on both Mercedes was illegally low.

Nico Rosberg, who eventually retired with an apparent engine failure, was found to be 1.1 PSI under the limit, while Hamilton’s left-rear was 0.3 PSI under.

It would not only be a clear technical breach to enhance performance, but also a safety issue, causing the highly experienced Pat Symonds of Williams to surmise that disqualification is the only possible penalty.

“I expect quite a big penalty — disqualification,” he said.

“It’s a safety issue, so yes (disqualification would be the penalty),” agreed Williams engineer Rob Smedley.

For his part, Wolff insisted Mercedes would not deliberately cut corners on safety, as the Brackley team is “always the first to be sure”. And Hamilton said a 0.3 PSI advantage would not be enough to help performance.

“That’s not the reason we won today,” he insisted.

And Wolff also revealed that tyres are pumped up in collaboration with Pirelli representatives, even though Smedley said Williams has fail-safe checks in place.

“We measure them (the tyre pressures) with Pirelli,” Wolff said on British television BBC. “At the moment we have no detail what is going on.”