Tom Watson, a Labour MP and key adversary of the Rupert Murdoch-owned paper during the Commons inquiry into phone hacking, tweeted: "Tomorrow's sun headline is "Boy, 4 has mark of the devil". Do you ever get embarrassed @rupertmurdoch? Please sort it out."

Other Twitter users expressed outrage. Some speculated the mark had been caused by a hairdryer burn.

Sagor

A M Dewhurst@scode83 wrote "The front page of The Sun has a story about a 4 year old boy supposedly having the mark of Satan. This is a mainstream newspaper people," while @sonofspeke tweeted: "The Sun soars away into the 17th century "Boy has Satan's Mark".

User @angledweb said: "The Sun is literally demonising a child on its front page. Surely that's abuse."A spokesman for the Sun said the story was provided by the parents, who had already publicised the pictures and story on Facebook. "We sought to treat it in a lighthearted fashion, highlighting the apparently fanciful link to the occult," he added.

The paper did not comment when asked whether or not the child's parents were paid. The spokesman's statement said instead: "We did not encourage the parents to embellish or expand the story; it came to us, and had already been the subject of discussion [raised by the parents] on social media. It's also worth noting that no concerns were expressed about the child's welfare.

"An unusual mark appears, the mother gets it checked out by a doctor who confirms there is no medical reason why it should be there, and discharges her. Social workers are not involved."

The story said the mark appeared on 23 May and had gone by 16 June.

Dr Evan Harris, a member of the campaign group Hacked Off, said that the editor's code clearly stated that consent must be obtained before a child's picture was used.

But Harris added: "The boy has a right to privacy and not to be bullied at school and, even though the parents have consented which gives the Sun legal cover, it is unethical to trample on those privacy rights. The Sun could have pixellated the boy's face and not provided the surname and still run the non-story."