A Home Office attempt to redraft controversial espionage legislation to tackle media concerns about its impact on investigative journalism has been greeted with scepticism across key parts of the industry. Ministers put down a series of amendments on Thursday aimed at eliminating concerns that the sweeping national security bill could be used to criminalise both reporters and whistleblowers. But media industry sources, briefed about the changes, said they believed the measures were only incremental and were discussing whether to press for the introduction of a public interest defence. “There’s a question whether these changes are sufficient to ensure protection for journalists enough to prevent prosecution,” one senior insider said, although any hope for a successful rebellion will depend on Labour support. Peers from several parties had voiced concerns last month that the bill could be used to suppress exposés of British military failures, such as concerns about the poorly armoured Snatch Land Rover, or abuses of power by the intelligence agencies. The key change proposed on Thursday is that a crime will have been committed if disclosure information or publication of a news story would “be likely to” materially assist a foreign intelligence service, ranging from the US’s CIA to Russia’s FSB. Previously the bill had said an offence carrying a prison term of up to 14 years would take if place if it “may materially” assist another country’s spy agencies – a wording so broad that Conservative peer Guy Black warned last month it could have a “chilling effect” on investigative journalism. One peer who had previously raised objections, the Lib Dem William Wallace, said on Thursday that “we need a public interest defence for journalists and researchers”. Such a clause would allow whistleblowers and journalists to argue that there was a wider value in disclosure or publication. Black, a deputy chair of Telegraph Media Group, is understood to be willing to bring forward alternative amendments to the bill, with the support of other media groups, including Guardian Media Group, the publisher of the Guardian. But without Labour backing the effort is doomed to fail and there is likely to be a period in which the industry will try to work out whether it is worth trying to press the case in the Lords or accept the government’s proposed revisions. A related government amendment seeks to clarify that a crime can only be committed if the journalist or whistleblower would have reasonably known of the risks at the time of disclosure by “having regard to other matters known to them”. Last month Black said journalism that risked falling foul of the initial version of the bill included the Panama Papers, which revealed how the global rich could exploit secretive offshore tax regimes; an account in the Mail of the “horrific experiences” of female submariners; and a BBC report about “a spy who used his status to terrorise his partner”. Other changes to the bill include narrowing the remit of the proposed foreign influence registration scheme to focus more clearly on political lobbying by foreign governments, to eliminate concerns it required businesses and charities to register legitimate engagement with foreign entities. Individuals, including MPs and peers, but also lobbyists and public relations professionals, will have to register whether they are working at the direction of any foreign government. Extra requirements will apply to an “enhanced tier” of countries, expected to include Russia and China.