add fuel to the flames is echar leña...
dar leña, meter leña, sacudir leña, and (most common, I find) meter caña are all pretty much the same thing: give someone a hard time, give them stick, etc. "Menudo repartidor de leña" is something I've heard people say about a fearsome Kung Fu fighter...
The only question is which English expression captures the tone, which is a subjective judgment. I thought about "give them a drubbing". This being El País and Aznar, there's definitely a sarcastic edge. He is, in their view (and mine, I have to say), a bit pompous, a bit schoolmasterish. There's a suggestion of how he personally will go down there and sort them out, stop them misbehaving. That's what you've got to try to capture, I think.

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Note added at 3 hrs (2010-12-22 07:43:24 GMT)
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Or maybe "sort out the Moroccans" or "bring the Moroccans into line". These are perhaps too free, but are expressions that might be used for taking someone outside and thrashing them, which is the idea.
Close to the original, in fact, could be "give the Moroccans a good thrashing" or "a good hiding". I quite like these because they fit the image of the old-fashioned schoolmaster.

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Note added at 3 hrs (2010-12-22 07:59:11 GMT)
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The next bit, "aunque por desdicha con retraso", is dripping with sarcasm; the subtext is something like: it's a bit late now; where was he when it was actually going on? And "patrióticamente"! They really, really don't like Aznar at El País.

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Note added at 3 hrs (2010-12-22 08:23:14 GMT)
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And "al moro", or course, is a very ex-colonial, not to say racist, way of putting it. Almost "the wogs" or "the fuzzy-wuzzies". But I think it'll have to be just "the Moroccans", and save the sarcasm for "dar leña".