Nick Griffin, the leader of the British National Party, has paid a secret visit to a First World War memorial in Belgium – only to become embroiled in an angry confrontation with a 13-year-old schoolboy, The Independent has learnt.

On Wednesday the pupil, William Robey, was in Ypres visiting the Menin Gate Memorial to the Missing as part of a school trip. It was built to commemorate the thousands of British and Commonwealth soldiers who died in the Ypres Salient in 1914-17, and its walls are inscribed with the names of 54,360 men who died for the British cause – including the 40th Pathans, an Indian infantry regiment which suffered great losses. But as "The Last Post" was about to be played, the schoolboy spotted Nick Griffin surrounded by some of his supporters.

William told The Independent: "I asked him if I could take his picture, next to the memorial for Pathan Indians. He reluctantly agreed, but as I went to take my photo I asked him, 'Isn't this against your party's policy?' One of his supporters put his hand over the lens, told me to 'get my facts straight', and grabbed my arm.

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"I took the picture but it's very blurry. I said to him, 'Your party's built on hatred.' He started shouting at me, pointing his finger. The rest of his lot were all laughing and smirking. I just felt a bit sick inside to see him there to be honest. There they were with their poppies on, trying to put this respectable front on, yet they're happy to confront a 13-year-old at a war memorial to try and get their point across.

"He was just saying 'I've got lots of Sikh friends' when my teacher stepped in and took me away."

A BNP spokesperson said Mr Griffin often visits War Memorials when he returns to the European Parliament. He said the BNP leader "doesn't recall any jostling,." He also "It wasn't one of Nick's security entourage who put his hand over the camera. It was someone else who was there."

William's mother, Lucy, said that since the incident her son had been approached by a number of people who wanted to congratulate him for "standing up against racism".

She added that William was "very into his politics" and "knew his stuff", hinting that he might have a career in public life ahead of him – although his talent for asking difficult questions of politicians suggests that a career in journalism might also beckon.