Hamilton stripped of pole position
Stewards took the decision to exclude the Briton from qualifying completely for the transgression after an investigation, meaning Pastor Maldonado, who finished second to Hamilton in qualifying for Williams, will now start from pole position, his first in Formula One. Ferrari's Fernando Alonso will join him on the front row at his home event.
McLaren had told the investigation that the fuel was below the expected levels because of 'force majeure' - a technical issue out of their control, but the stewards dismissed this argument.
The team later confirmed through a spokesman that they had accepted the verdict.
"We accept that the stewards did not agree with our interpretation of force majeure," a spokesman told Autosport. "Our aim is now to maximise the points we can score tomorrow."
Hamilton had blown the field away with his final effort - a 1:21.707 - which was almost six-tenths clear of his nearest challenger.
But having completed the lap he was instructed by his team to pull up on the track, with his race engineer suggesting over the radio there was a technical problem with the car. Team principal Martin Whitmarsh subsequently confirmed that Hamilton only had 1.3 litres of fuel left in the tank when the Brit parked on the Circuit de Catalunya, meaning that the McLaren did not have enough to return to the pits and provide a full one litre fuel sample as stipulated by the FIA rules.
"The stewards received a report from the Race Director which stated that during post-qualifying scrutineering a sample of fuel was required from car 4, however, the car failed to return to the pits under its own power as required under Article 6.6.2 of the FIA Formula One Technical Regulations," said the stewards in a statement.
"The Stewards heard from the team representative Mr Sam Michael who stated that the car stopped on the circuit for reasons of force majeure. A team member had put an insufficient quantity of fuel into the car thereby resulting in the car having to be stopped on the circuit in order to be able to provide the required amount for sampling purposes.
"As the amount of fuel put into the car is under the complete control of the Competitor the Stewards cannot accept this as a case of force majeure.
The rules on under-fuelling were reviewed after a similar incident involving Hamilton at the 2010 Canadian Grand Prix. On that occasion Hamilton was reprimanded and his team fined $10,000, but he kept his place on the grid.