Police are assessing a video in which Islamist militants threaten attacks on shopping centres in the US, Canada and the UK.

It appears to have been posted by Al Shabaab - the group which was responsible for the 2013 attack on Westgate shopping mall in Nairobi that killed 67 people.

Oxford Street and 2 Westfield shopping centres in London are mentioned.

Terror expert Dr Sajjan Gohel says there's nothing to suggest an attack's imminent but it shouldn't be dismissed: