Stewards are to review Lewis Hamilton's pole position for the Spanish Grand Prix, after it emerged that the British driver had been ordered to park the car out on track on its in-lap because of a lack of fuel.

According to reports from the Circuit de Catalunya in Barcelona, Hamilton's car only had 1.3 litres left in the tank after setting a scintillating pole position time of 1:21.707s in the closing minutes of Q3, to put him half a second ahead of Williams' Pastor Maldonado.

But it takes around two litres to complete an in-lap, and in addition FIA rules require a further litre of fuel to be in the tank to be available for sampling as part of the post-session technical inspection process. An "operational error" in the McLaren garage is said to be to blame for the underfueling.

"There was enough fuel to take a fuel sample but we stopped the car and are now talking to the stewards about that," was the view of team principal Martin Whitmarsh.

But unless McLaren can satisfy the FIA stewards that the car has a provable, legitimate excuse for stopping out on track for a technical reason and not simply because of a lack of fuel, Hamilton could find his lap time deleted.

Whitmarsh insisted that the problem was indeed genuine and that the team had the evidence to prove it: "It happened in the garage [but it] didn't impede the performance in any way."

It's not clear what penalty would be applied if the stewards are unconvinced by McLaren's representations. If Hamilton were to have his fastest lap deleted and his original laptime reinstated then he would be moved back to sixth place, the equivalent of a five place grid penalty. Other possible sanctions could see him given a ten place penalty or even sent to the back of the grid altogether.

Any penalty is likely to promote Maldonado to pole, with Ferrari's Fernando Alonso alongside him on the front for for his home Grand Prix.

The scenario of stopping an under-filled car out on track so that it doesn't fail post-session inspection originally arose in Canada in 2010, after which race director Charlie Whiting issued a technical directive to all team stating that "Any team whose car stops on the slowing down lap after the race will be asked by the stewards to explain why this happened.

"If they are not satisfied that the reasons were beyond the control of the driver or team, and feel that this has been done deliberately to gain a competitive advantage, appropriate action will be taken," the directive added.

A penalty would be a crushing blow for Hamilton, who clearly dominated qualifying right from the start despite unexpectedly stuff competition from Maldonado.

"It was a massive margin," said Whitmarsh of Hamilton's pole position time. "He undoubtedly deserves to be there."

Hamilton had an earlier encounter with the stewards in a row over an incident with Michael Schumacher in the morning Free Practice 3 session, during which Michael Schumacher's Mercedes appeared to return to the track right in front of the McLaren and impede a flying lap by Hamilton. However, the stewards declined to take any further action over the incident.