A Nominet spokesman said: “We have suspended this website for breaching our terms and conditions.
“The website did not conduct suitable age verification as required under the Online Safety Act – and we have advised the domain owner and its registrar.
“The web address featured in this popular children’s book series had been allowed to expire by the previous owner and was subsequently purchased by a third party.
“It is recommended that those using web addresses in prominent locations continue ownership of the domain to avoid issues like this.”
On Wednesday Puffin Books confirmed the website had once been owned by Cope but had been taken over.
In a statement, the firm and the author said the sale and distribution of the books had been paused and they had been in contact with retail and educational partners about temporarily removing the books.
It led to schools advising parents to remove the books immediately and bring borrowed copies back to school.
Puffin and Cope have been approached for a new comment.