The former head of MI5 has called for social media firms to face tighter regulations as she described the mass harvesting of personal data as "very worrying".

Dame Stella Rimington, who was the first female head of the security service, said the general public probably did not realise how much private information they disclose online.

Social media giants are facing increasing scrutiny about how they handle and protect the data given to them by users on their sites amid fears it can be exploited by third parties.

Facebook received widespread censure last year for the role it played in the Cambridge Analytica scandal, in which sensitive information about 87 million was used for political purposes.