Watching streamed extremist material online will be a criminal offence under plans to crackdown on terrorist propaganda.

Home Secretary Amber Rudd will say those found guilty of repeatedly viewing terrorist material could face up to 15 years in jail.

The new law will extend an existing ban on downloading and possessing the content on a PC to repeatedly watching it through sites like YouTube.

Ms Rudd said: “I want to make sure those who view despicable terrorist content online including jihadi websites, far-right propaganda and bomb-making instructions face the full force of the law.

“Changes will enable police and the security service to keep pace with modern patterns of internet use and intervene earlier in an investigation given the speed with which online radicalisation is taking place.”

The move comes as Ms Rudd ramped up her calls for internet giants such as Google and Facebook to do more to tackle the scourge of online extremism.

The Home Secretary yesterday criticised firms for developing encrypted software that has held back the authorities from investigating suspicious activity.

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End-to-end encryption is used in a variety of the most secure messaging apps, including those made by Apple, WhatsApp, Signal and Telegram.

The government has said that it is concerned that the technology keeps them from reading terrorists' and criminals' messages – but experts warn the same technology also keeps private citizens from having their messages read by criminals, and is used to secure banking technologies, among other functions.

Ms Rudd told a fringe event at Conservative conference that companies need to step up at a time where terrorist tactics are at a “whole new level”.

“The tech giants need to step up and do more, take a moral responsibility for the fact their platforms are being used in this way,” she said.