The second part of the Leveson inquiry, which was due to investigate the extent of crimes committed at News International and other media organisations, may not go ahead, Lord Justice Leveson has indicated.

In a ruling posted on the Leveson website late on Tuesday night, the judge said such an inquiry "will involve yet more enormous cost" to the public and participants and would be required to "trawl over material then more years out of date".

The Leveson inquiry has until now been restricted from investigating the extent of crimes such as phone hacking or police corruption because of the risk of prejudicing potential criminal trials.

It was therefore intended a second inquiry would take place - possibly in a year or 18 months - when all possible criminal trials were complete.

Leveson said he has not ruled out a second inquiry, but has indicated his preference was to make the present inquiry as broad as possible to reduce the need for a second.

"Obviously, the more restrictive in its analysis that Part 1 has been, the greater will be the legitimate public demand for Part 2," he said.

Leveson said police inquiries were extensive and a potential part two would be "delayed for very many months, if not longer".

"In those circumstances, it seems to me that it is in everyone's interests that part one goes as far as it possibly can.

"If the transparent way in which the inquiry has been conducted, the report and the response by government and the press (along with a new acceptable regulatory regime) addresses the public concern, at the conclusion of any trial or trials, consideration can be given by everyone to the value to be gained from a further inquiry into Part 2."

Sources say Leveson has not abandoned the idea of a second inquiry but

used the ruling to lay down a marker that it needed to be discussed.

Leveson's remarks were part of a ruling on the extent to which he can go with his conclusions and recommendations in his final report.

Last month, barristers for the tabloid newspapers and the police had argued he should be restricted from naming newspapers.