Chinese state operatives present a daily national security threat to the UK, the head of MI5 Sir Ken McCallum has said, BBC reported.

In a speech, he said MI5 had intervened operationally to disrupt Chinese activity of national security concern in the past week.

Addressing a row over the collapse of a case involving alleged spying on behalf of China in the UK, Sir Ken said the alleged activity was disrupted by MI5 and that it was "frustrating when prosecutions fall through".

The government and the Crown Prosecution Service (CPS) are facing questions over the collapse of the case, according to BBC.