British spies will launch a counter-propaganda war against the Russians as part of a major overhaul of the UK's security capabilities announced by Theresa May.

The Prime Minister has instructed the intelligence services to use social media to disrupt misinformation as she promised to use "every capability at our disposal" to defeat the new threat facing Britain.

As well as increased Russian aggression, sources warned the Islamist terror threat is likely to rise in the next two years as Mrs May revealed a major new effort to ensure every Government agency and department views national security as their priority, rather than just police and security services.

The plan, dubbed the Fusion Doctrine, aims to tackle the evolving threats posed by cyber warfare and so-called fake news as well as bombs.

Security experts on Tuesday warned President Putin's Government has pumped out over 20 different stories to explain the Salisbury attack so far in a bid to "confuse the picture and confuse the charge sheet."

They said the UK's soft-power capabilities and ability to counter propaganda online will form part of the new front line.