Lord Justice Leveson warned against leaks today after a Labour MP quoted from a document that had not been publicly released by the inquiry.
Chris Bryant suggested in the House of Commons yesterday that David Cameron may have misled Parliament when he said he only met Rupert Murdoch once between May 2010 and July 2011.
Raising a point of order, the MP said: "Rupert Murdoch - this has been published by the Leveson Inquiry - made it clear that there were meetings with the Prime Minister on May 18, May 25, July 21, another on July 21, and July 22."
In fact no such information had been released by the inquiry on its website at that time.
Bryant is a "core participant" in the Leveson Inquiry, meaning he has advance access to documents and witness statements via a secure computer system called Lextranet.
Lord Justice Leveson said today: "Core participant status is not intended to provide an advantage to core participants, and so permit them to publish material before it is available for publication by those who are not core participants."
He added: "For the avoidance of doubt, nobody should be publishing anything using the material from Lextranet, which is intended to be only to provide core participants with fore-warning of statements and exhibits.
"Everyone must understand that it is only the redacted statements or exhibits that can ever be published or referred to."
Lord Justice Leveson said he has redrafted his order banning publication of material before it is posted on the inquiry's website to make it clearer.
"The new order will be placed on the website immediately and I will treat any breach of it as a matter of real significance," he said.
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