The Sun has warned Theresa May that local newspapers will be “stripped of almost all news value” if it goes through with proposed changes to the law on libel costs.

The tabloid has urged the Prime Minister to fight and stop the implementation of Section 40 of the Crime and Courts Act 2013, which could see publishers forced to pay both sides’ costs in libel or privacy actions even if they successfully defend a case in court.

In a leader column in yesterday’s newspaper, The Sun claimed Mrs May’s years in Downing Street would go down in history as the “profoundly illiberal era in which 300 years of the free press in this country was ended” if the change to the law was made.

It also echoed the warning by Scottish Newspaper Society director John McLellan, who last week described the legislation as “Government-sanctioned blackmail”.

The leader read: “Today, the Sun appeals directly to Prime Minister Theresa May: Do not let this historic calamity happen on your watch. It is state-sponsored blackmail – newspapers either agree to be regulated by politicians or risk paying through the nose for every story we print, even if it’s verifiably accurate.

“The implications are far-reaching and fearsome. Local newspapers, already on financial life-support and petrified of legal action, would be stripped of almost all news value. Investigative journalism would cease overnight as the fear of litigation outweighed any pride in exposing wrongdoing.”

The Government-backed Press Recognition Panel will meet today to decide whether to approve an application by Impress to become the recognised press regulator even though only a handful of micro-publishers have signed up to it.

The Independent Press Standards Organisation (IPSO), to which most UK newspaper publishers have opted to subscribe, has made clear it has no intention of applying for recognition on the grounds that it amounts to state-sponsored regulation of the press.

The Sun’s leader continues: “Those in the public eye who object to a story published about them could punish media outlets with huge court bills, even if the story is justified and proper.

“So we say this to Theresa May: You must fight this and you must stop it. If you don’t, your years in Downing Street, whatever else they are remembered for, will go down in history as the profoundly illiberal era in which 300 years of the free press in this country was ended.”