Stewards stripped Lewis Hamilton of pole position for the Spanish grand prix.
"This is such a disappointment. Today's qualifying session was one of the best I've ever driven," said the 2008 world champion, who has been relegated to the very back of the grid.
His McLaren engineer had instructed him to stop on the track with a "problem" after completing his pole lap.
It emerges that the team was worried Hamilton would not have enough fuel left in the car for the mandatory 1 litre FIA sample.
But rule 6.6.2 requires drivers to return to the pits after qualifying under their own power.
Sam Michael, the sporting director, argued a case of 'force majeure'.
The stewards said in a statement: "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."
"Since we accept that the stewards didn't agree with our interpretation of force majeure, we didn't contest their decision to penalise him," said team boss Martin Whitmarsh.
It means Pastor Maldonado inherits his first pole; the first for Williams since Nico Hulkenberg in 2010.
UPDATE: Following Hamilton's penalty the whole of the paddock reacted.
The Sun newspaper refer to the incident as a draconian "24-place grid penalty" imposed by the FIA after an "astonishing cock-up" by McLaren.
Writing in the Telegraph, Tom Cary said the severity of the disqualification "raised eyebrows", but agreed that "McLaren's mistake was horrendous".
He said it has been "a season of errors" by the famous British team, who are yet to get Hamilton's signature on a new contract beyond 2012.
"Hamilton must be seething," read an article in the Daily Mail newspaper, while The Times laid out McLaren's "catalogue of errors".
27-year-old Hamilton's "raw talent is being thwarted by mishap and cock-up," said journalist Kevin Eason.
"McLaren are lovely people but how the hell do they get themselves in this position?" wrote the Mirror's Byron Young on Twitter.
Even the non-English language media agreed.
"It was another great mistake by McLaren that could eventually cost Hamilton the championship," wrote Livio Oricchio in O Estado de S.Paulo.
Italy's La Stampa called McLaren's fuel gaffe a case of "harakiri".
Germany's Auto Motor und Sport added: "It was error number 13 for McLaren since last year".
While highly critical of McLaren's own-goal, however, the feeling in the paddock is that the stewards' penalty - although accepted by McLaren - was overly harsh.
"Back of the grid? Way, way too harsh", added Young on Twitter.
"Draconian penalty in my view," agreed PA Sport's Ian Parkes. "Dropping Q3 time would have sufficed."
Sky commentator Martin Brundle added: "(I) feel they should have deleted that (Q3) laptime only which would have put him sixth".
And excluding Hamilton from Q3 altogether would have put him 11th. Now, he will be "lucky to score a point", Auto Motor und Sport predicted.
In the Independent, however, David Tremayne noted: "Welcome to the draconian world of F1."
David Croft, the lead Sky commentator, said the FIA stewards had acted correctly.
"A good rule should be one that covers all eventualities with a penalty that acts as a deterrent which in this case is what happened.
"Too little fuel can't be tolerated," he added. "It seems harsh but had Lewis taken pole by one thousandth of a second, would it be harsh then?"
The Spanish fans - not Hamilton's biggest supporters dating back to his spats with Fernando Alonso in 2007 - were happy.
Asked on the El Mundo website whether the penalty was fair, 76 per cent answered yes.