Lewis Hamilton was on Saturday stripped of his pole position for Sunday's Spanish Grand Prix, following a stewards meeting that decided he had stopped on track after qualifying in order to save fuel.

The stewards said Hamilton had insufficient fuel in his McLaren car and, as a result, he will start Sunday's race from the back of the grid.

Hamilton, the 2008 world champion, had claimed pole position with a dazzling lap in the final part of the top-10 shootout Q3, outpacing nearest rival Venezuelan Pastor Maldonado of Williams by half a second.

But he stopped on track on his slowing down lap and was assisted back to the parc ferme where a fuel sample was taken from his car. The stewards ruled that this was irregular and relegated him to the back of the grid.

Maldonado, 27, has never previously started a race in better than the seventh position on the grid he occupied for the 2011 British Grand Prix.

Moments before the decision was revealed, McLaren team chief Martin Whitmarsh conceded that Hamilton was likely to lose his pole position.

Whitmarsh declined to explain precisely why the team asked Hamilton to stop, but accepted that McLaren would likely be penalised if it was felt they were taking advantage of an opportunity to save fuel.

That suggested that Hamilton may have been running so low on fuel that the team feared he could have failed to make it to parc ferme and have sufficient fuel remaining to supply a sample to the stewards.

"There was enough fuel to take a fuel sample, but we stopped the car. There was 1.3 litres of fuel taken out of the car," said Whitmarsh.

Under the rules laid down by the sport's ruling body the International Motoring Federation (FIA), drivers must return to parc ferme under their own power with a minimum of one-litre of fuel on board.

It is not acceptable for them to stop to save petrol for the sample as that would give them a competitive advantage, permitting them to run with less fuel, and hence less weight, in qualifying.

Hamilton and McLaren were given a reprimand and a $10,000 fine at the 2010 Canadian Grand Prix in similar circumstances.

Whitmarsh said Saturday's drama was due to a problem in the McLaren garage.

"It is a technical problem that happened in the garage that didn't impede the performance of the car in any way and we stopped when it had 1.3 litres of fuel in the car," he added.

He was adamant that Hamilton had enough fuel to complete his lap back to the pit lane and also to supply a one litre sample.

Hamilton, 27, had a best lap of 1min 21.707sec to finish half a second clear of Maldonado.

Fernando Alonso was next fastest ahead of Romain Grosjean and his Lotus team-mate Kimi Raikkonen.

They were followed by Sergio Perez of Sauber, Nico Rosberg of Mercedes and, unexpectedly, defending champion Sebastian Vettel in his Red Bull.

For Williams, Maldonado's promotion to pole was a great present for team founder Sir Frank Williams, who was celebrating his 70th birthday in the team garage.

"We have worked so hard to understand these tyres and develop our car around them and this is a great step forward for the team. We have such a good spirit and the car feels fantastic," said Maldonado.