The school said no one has been bitten by the spider but local health authorities have advised it to close for the day to deal with the infestation.
Experts say the Steodata nobilis, a species of the false widow, are becoming more common in the U.K. and are the most dangerous of the 12 species of biting spiders known in Britain.
But they stress that spider bites are rare in Britain, and in most cases the symptoms are mild. The spider's bite may sting, swell up or cause discomfort like a wasp sting, but has not been known to cause deaths.
"They're not aggressive spiders, they don't seek out humans," said David Lalloo, a professor at the Liverpool School of Tropical Medicine.
"Most people won't get much of a reaction. Some people may feel a bit unwell for a day or two, but that's very rare," he said.
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