The terrorism legislation watchdog has likened Theresa May’s proposals to punish companies such as Facebook and Google for failing to tackle extremist propaganda to China’s strict regime of internet censorship.

Max Hill QC, the independent reviewer of terrorism legislation, said internet companies should be “brought firmly onside” rather than threatened with fines.

In a speech delivered at the Terrorism and Social Media conference in Swansea, reported in the Times, he said: “I struggle to see how it would help if our parliament were to criminalise tech company bosses who ‘don’t do enough’. How do we measure ‘enough’? What is the appropriate sanction?

“We do not live in China, where the internet simply goes dark for millions when government so decides. Our democratic society cannot be treated that way.”

May outlined the idea of punishing companies such as Facebook, YouTube and Google if they fail to remove extremist propaganda and terrorist material from their platforms in the wake of the Manchester Arena bombing.

After a meeting with the French president, Emmanuel Macron, in June, May said they were both determined to ensure the internet could not be used as a safe space for terrorists and criminals.

The UK and France are to develop plans to create a new legal liability for tech companies that fail to take action against unacceptable content.

Speaking at the time, May said: “The counter-terrorism cooperation between British and French intelligence agencies is already strong, but President Macron and I agree that more should be done to tackle the terrorist threat online.

“In the UK we are already working with social media companies to halt the spread of extremist material and poisonous propaganda that is warping young minds. I can announce that the UK and France will work together to encourage corporations to do more and abide by their social responsibility to step up their efforts to remove harmful content from their networks, including exploring the possibility of creating a new legal liability for tech companies if they fail to remove unacceptable content.”