Here you go: Section 43/44 of the Terrorism Act 2000
It is not an offence to photograph or film in public areas The police CAN stop and search you: In public if they suspect you of being a terrorist; In a sensitive area without suspicion The police CAN view images on a phone or camera to determine any link to terrorism. The police CAN seize anything, including phone or camera that may be evidence of you being a terrorist The police CANNOT destroy images or film The police CANNOT read text messages, emails or voicemails The police CANNOT prevent photography in a public place or of themselves.
If you are arrested of course, one or two of the above wouldn't apply, I suspect.
What's any of that got to do with posting videos of people online?
Absolutely nothing, James. But the question was raised of the lawfulness of photographing or filming in a public place. Thought it may be interesting to post what your rights are in the UK considering some countries ban the use of dashcams. And quoted the Terrorism Act because of recent events.