A key adviser to Lord Justice Leveson claims his last-resort option for compulsory press regulation if they did not join voluntarily could be illegal.

The judge's report recommended an independent self-regulatory body for the industry backed up by legislation.

But, if newspapers did not sign up to that, he said politicians might need to consider compulsory regulation.

Liberty's Shami Chakrabarti said she could not support this as it would breach the Human Rights Act.