Downing Street has insisted the freedom of investigative journalists and whistleblowers will not be restricted, after the Law Commission published plans suggesting that maximum jail terms for those leaking information should rise from two years to 14.

No 10 said it was incorrect to suggest that either group would face greater threat of prosecution as a result of the new proposals, which have been condemned by prominent whistleblowers and civil rights groups.

Theresa May’s official spokesman said: “I’ve seen the way this has been reported and it is fundamentally wrong. It is not, never has been and never will be the policy of the government to restrict the freedom of investigative journalism or public whistleblowing.

“One of the points of this review is to consider whether more safeguards are required to protect public sector whistleblowers and journalists.”

Asked whether journalists could face jail for reporting leaked information, he said: “We will not do anything to restrict the freedom of journalists.”

The government’s legal advisers were accused of launching a “full-frontal attack” on whistleblowers on Sunday over the proposals, which recommend radically increasing prison sentences for revealing and handling state secrets.

Draft recommendations from the legal advisers say the maximum prison sentence for leakers should be raised, potentially from two to 14 years, and the definition of espionage should be expanded to include obtaining sensitive information, as well as passing it on.

Media organisations and civil rights groups have also expressed alarm at the Law Commission’s assertion that they were consulted over the plans, when they say no substantial discussions took place.

The Guardian, the human rights group Liberty and campaign body Open Rights Group are among a series of organisations listed by the Law Commission as having been consulted on the draft proposals, but all three say they were not meaningfully involved in the process.

The Law Commission says on its website that in making the proposals, it “met extensively with and sought the views of government departments, lawyers, human rights NGOs and the media”. The law commissioner, Prof David Ormerod QC, said: “We’ve scrutinised the law and consulted widely with ... media and human rights organisations.”

But Liberty said that while a meeting was held, it was “not on the understanding that this was a consultation”. A source said: “Liberty do not consider themselves to have been properly consulted. And we will be responding in detail to the [public] consultation.”

Cathy James, the chief executive of Public Concern at Work, was also surprised to see her the whistleblowing charity listed as being involved.

She said: “I didn’t actually know we were listed in the document as we have been working our way through it so it is a big surprise to me. I believe my colleague met with them initially but we were not consulted in the normal sense of the word consultation. That is not what happened.

“We are very worried about the extent of the provision in the recommendations both for whistleblowers and public officials. It’s a huge backward step and we are very worried.”

A Law Commission spokesman told the Guardian: “We are currently conducting an open public consultation on the protection of official data, including the Official Secrets Acts.

“We are seeking views on how the law could meet 21st-century challenges while also ensuring people don’t inadvertently commit serious offences. Our provisional proposals make a number of suggestions to improve the current laws around the protection of official data, and we welcome views.”