Alfa Romeo has suggested human error may be at the heart of the fuel issue that resulted in Valtteri Bottas being excluded from the qualifying classification for the British Grand Prix.

Bottas stopped on track during the first qualifying session at Silverstone, with his car later unable to provide the required one-litre sample of fuel once it was returned to the garage.

Bottas had set a time good enough to get him into Q2 but following an investigation by the FIA, they were left with no choice but to disqualify the Finn from the standings, with Alfa Romeo unable to provide any mitigating circumstances.

The team initially suggested it was a technical issue but head of trackside engineering Xevi Pujolar has now implied otherwise.

“We had a problem on the fuelling side,” said Pujolar. “We didn’t have enough fuel.”

As to how such an incident could happen, Pujolar added: “This is something we are discussing internally because both cars had the same plans, the same programme, and they were in the same condition.

“But obviously one of the cars didn’t have enough (fuel).”

Suggested to Pujolar it was ‘human error, something you don’t understand’, he replied: “Yeah.”

For this weekend, the C43s of Bottas and team-mate Zhou Guanyu are sporting a raft of upgrades that include a new floor, rear suspension and diffuser.

Bottas has indicated the car has taken “a step”.

“I definitely feel the step, and in qualifying we managed to extract a bit more with the set up,” he said.

“It seemed like it needed a different set up in terms of ride height and everything, so the car actually felt a step.

“Hopefully (in the race) we get a better picture.”

Describing the specifics of the actual ‘step’, Bottas added: “More high-speed load basically without affecting the low-speed performance.”