London: His mother, Nicola Scholes, a primary school teacher, posted photographs on her Twitter page, showing her son posing in his outfit while brandishing cable ties and a blindfold, props used by Grey in the novel's more risque passages.
Underneath she wrote "Offensive costume. Excluded from photos, told to change yet teacher dressed as a serial killer and others with guns?"
The schoolboy claimed that the stunt was "a bit of fun" that had got out of hand.
"I thought personally I didn't want to go as a cartoon character, so I chose Christian Grey just to have a bit of fun," he told the local Manchester Evening News.
"A lot of fuss has been made over nothing."
His mother on Friday said that her son had not read the book or seen the recently released film, but was "aware that the book contains things of a sexual nature."
"Liam's argument was it's the most talked about book character in the last couple of years," she told BBC Radio 4's Today programme.
"Apparently it went down really well with the vast majority of the students, they all took it for the tongue-in-cheek joke that it was meant to be.
"They (teachers) wanted him to be James Bond who ironically is a very promiscuous character who kills people so I don't know which is worse of the two."
She pointed out that a teacher had come as US fictional serial killer Dexter.
School headteacher Lynn Nicholls said her decision "reflected the school's high standards in terms of student behaviour, welfare and safeguarding", and denied he had been banned from all the celebrations.
"His costume was modified and he was then able to fully participate and enjoy the day with his peers," she said.
A British boy got in trouble at school when he arrived for World Book Day celebrations dressed as the lead character from racy novel "Fifty Shades of Grey", complete with bondage equipment.
While other youngsters marked Thursday's event by dressing up as Harry Potter, Willy Wonka or Paddington Bear, the 11-year from Manchester, northwest England, was slicking back his hair and dusting down a sharp suit as worn by the fictional billionaire Christian Grey.
But his efforts left teachers at Sale High School unimpressed. They banned him from group photographs and told him to alter his outfit, the school said.
Underneath she wrote "Offensive costume. Excluded from photos, told to change yet teacher dressed as a serial killer and others with guns?"
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"I thought personally I didn't want to go as a cartoon character, so I chose Christian Grey just to have a bit of fun," he told the local Manchester Evening News.
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His mother on Friday said that her son had not read the book or seen the recently released film, but was "aware that the book contains things of a sexual nature."
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"Apparently it went down really well with the vast majority of the students, they all took it for the tongue-in-cheek joke that it was meant to be.
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She pointed out that a teacher had come as US fictional serial killer Dexter.
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"His costume was modified and he was then able to fully participate and enjoy the day with his peers," she said.
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