Archbishop of Canterbury Rowan Williams, spiritual leader of the world's 77 million Anglicans, said Gibbons' prosecution and conviction was "an absurdly disproportionate response to what is at worst a cultural faux pas."
Foreign Secretary David Miliband summoned the Sudanese ambassador late Thursday to express Britain's disappointment with the verdict. The Foreign Office said Britain would continue diplomatic efforts to achieve "a swift resolution" to the crisis.
Gibbons was arrested Sunday after another staff member at the school complained that she had allowed her 7-year-old students to name a teddy bear Muhammad. Giving the name of the Muslim prophet to an animal or a toy could be considered insulting.
The case put Sudan's government in an embarrassing position - facing the anger of Britain on one side and potential trouble from powerful Islamic hard-liners on the other. Many saw the 15-day sentence as an attempt to appease both sides.
In The Times, columnist Bronwen Maddox said the verdict was "something of a fudge ... designed to give a nod to British reproof but also to appease the street."
Britain's response - applying diplomatic pressure while extolling ties with Sudan and affirming respect for Islam - had produced mixed results, British commentators concluded.
In an editorial, The Daily Telegraph said Miliband "has tiptoed around the case, avoiding a threat to cut aid and asserting that respect for Islam runs deep in Britain. Given that much of the government's financial support goes to the wretched refugees in Darfur and neighboring Chad, Mr. Miliband's caution is understandable."
Now, however, the newspaper said, Britain should recall its ambassador in Khartoum and impose sanctions on the Sudanese regime.