"Creating apps like Signal could be considered 'hostile activities' under new Counter-Terrorism and National Security Acts, UK watchdog warns"
The language changes here are slight (claims -> warns) and includes more context about the reason this watchdog is speaking out (current debates around the Counter-Terrorism and Border Security Act, new implementation of the National Security Act), using language from the first 4 paragraphs (may be considered, could be considered, stark warning, report warns, etc).
You could also leave out the specific names of the acts—they're not super helpful to me as a non-UK news consumer, but I suspect they might be more crucial to someone who's tapped into the UK political news cycle:
"Creating apps like Signal could be considered 'hostile activities' under new laws, UK watchdog warns"
Although I'm not actually sure how much the watchdog is "warning" here, despite the article claiming it is. The language from the report is the following:
journalist may be more sinister than first appears, so permitting an officer to examine whether the individual is a witting or unwitting agent of a foreign state might be described as necessary in the right circumstances. Serious responsibility is placed on police to use the power wisely.The report doesn't make any recommendations or suggest any changes to the law, it seems to consider that it is good that this could be considered Section 3 "hostile activity". This later part about Schedule 3 investigations also makes this clear: