A Spanish cartoonist faces a possible jail term for insulting the Crown Prince in a graphic drawing that has shattered one of the country’s greatest taboos.

Spain’s National Court ordered police to seize all 400,000 copies of the weekly satirical magazine El Jueves from newspaper kiosks, as well as the “printing plates”. Judge Juan del Olmo also ordered the magazine to identify the cartoonist responsible for its latest cover, which was met with disbelief in a nation where even the smallest criticism of the Royal Family is deemed off-limits.

It depicted the heir to the throne, Prince Felipe of Asturias, having sex with his wife, Princess Letizia, and saying: “Do you realise that if you get pregnant . . . It will be the closest thing to work I’ve done in my life?”

The drawing referred to a recent decision by the Government to award mothers €2,500 (£1,680) for each child they bear. Insulting royalty or “damaging the prestige of the Crown” is a crime in Spain, punishable by up to two years in prison.

The public prosecutor’s office said in its writ that the cartoon was “clearly denigrating and objectively libellous”. The court also planned to issue an injunction to stop websites or other media from reproducing the cartoon.

The cartoonist, who goes by the name Guillermo, expressed his amazement. “They’re going to take the printing plates? Why those haven’t existed for years!” he said, before joking: “The best thing would be for them to cut off my right hand.”

King Juan Carlos won the respect of a generation of Spanish newspaper editors when, in 1981, he intervened to halt a military coup against the fledgeling democratic Government.

Although journalists have always gossiped about his personal and business affairs, almost nothing has made it into print since he was crowned in 1975 after the death of the dictator General Franco. But many people believe that Spain’s three-decade taboo against criticising the Royal Family is on the point of collapse, with a huge public appetite for gossip being met increasingly by internet sites that are harder to control.

Tongues were set wagging when Prince Felipe married Letizia Ortiz, a divorced commoner and former television journalist, in 2004. When Letizia’s sister died earlier this year, many newspapers disregarded pleas by the Royal Family to be discreet and mentioned police theories that she committed suicide.

The judicial ruling last night set off a political storm in Spain, with the United Left party calling it “excessive and anachronistic” and judges defending it as “prudent” and “respectable”. Some Spanish internet users supported the ban, saying that the cartoon had been in poor taste, while others said that freedom of speech must be protected. Several recalled that some Spanish newspapers had reproduced the Danish cartoons of Prophet Muhammad in 2006 that caused worldwide protests by Muslims.

The ruling “shows that we still lack political maturity,” Julio Rey, a cartoonist for El Mundo newspaper, said. “It’s terribly important for the system to be able to laugh at itself.”

Not all cartoonists leapt to their defence. “I think our colleagues have gone too far,” said José María Varona, the vice-president of the Spanish Federation of Cartoonists. “This has nothing to do with the cartoons of Muhammad. The cartoon is completely beyond the pale.”

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