Hamilton's Spanish Grand Prix pole position hanging in the balance

Hamilton secured McLaren's 150th pole position at the Circuit de Catalunya on Saturday, but shortly after taking the chequered flag he was ordered to stop by the team because of an unidentified problem.

Under the rules, drivers are supposed to return to parc ferme under their own power and with a minimum of one-litre of fuel on board to be able to supply a sample to the FIA.

It is not acceptable for drivers to stop early simply to save petrol for the sample - because that would give them a competitive advantage as they could run with less fuel, and therefore less weight, during their qualifying lap.

Following a directive issued at the 2010 Canadian Grand Prix, after Lewis Hamilton and McLaren were given a reprimand and a $10,000 fine for stopping deliberately on a slowing down lap after qualifying to save fuel, the FIA has made it clear that only genuine technical problems would be acceptable.

FIA race director Charlie Whiting said in a note issued on race morning in Canada: "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."

Whitmarsh would not expand on the reasons for Hamilton being told to stop, but said that the FIA had been able to take its sample.

"There was enough fuel to take a fuel sample, but we stopped the car - and we are now talking to the stewards about that," he explained. "There was 1.3-litres of fuel taken out of the car."

Rules state that cars must have one litre of fuel onboard.

"Competitors must ensure that a one litre sample of fuel may be taken from the car at any time during the Event.

"Except in cases of force majeure (accepted as such by the stewards of the meeting), if a sample of fuel is required after a practice session the car concerned must have first been driven back to the pits under its own power."

When asked if he was confident about Hamilton's pole position standing, he said: "I don't know. But I hope so - Lewis did a fantastic job throughout that session and we have all seen how difficult it is at the moment to be consistent, to switch everything on at the right time.

"Lewis and his team did a great job, so it was a massive margin by the situation within F1 at the moment so undoubtedly he deserves to be there."

Whitmarsh refused to be drawn on offering any insight into the reasons behind Hamilton being given the order to stop.

But a suggestion that the problem was in the pits rather than on the car could point to a problem in the pits meaning not enough fuel went into the car ahead of his final run.

"It is a technical problem that happened in the garage that didn't impede the performance of the car in anyway, and we stopped the car when it had 1.3-litres of fuel in the car," said Whitmarsh.

He added: "There was a technical problem that led to that situation. I think it is not for me to decide; but I would believe that to be a force majeure but it is up to the stewards to decide."

Whitmarsh was adamant, however, that Hamilton had enough fuel in the car to be able to complete his in-lap and supply the one litre sample.