Nearly a decade ago, London's response to a terror attack was a resolute: Keep calm and carry on.

But after a spate of recent attacks, including the deaths of children and families at a concert in Manchester last month, the first sign of a crack in the determined British demeanour was contained in a social media post from the Metropolitan Police service, sent to its nearly 900,000 followers: "RUN, HIDE, TELL."

It captures the fear, terror and panic now threatening to overwhelm the UK as a series of incidents suggest it is facing an ongoing threat of terror attacks.

Instructions contained in the social media post appear to suggest a greater sense of urgency: