Thanks for clarifying. I don't think that's the correct interpretation though. The government advice for tier 4 says:
> You must not leave or be outside of your home except for where you have a specific purpose, or a ‘reasonable excuse’
> If you live in a tier 4 area, you must stay at home. You must not leave your home to travel unless for work, education or other legally permitted reasons
So when Boris says "should" I believe he means "must unless you are in one of the excluded categories".
Isn't that single webcam image consistent with essential workers? The trucks are surely not banned; and it's understandable that people have to go home on a Friday night.
> You must not leave or be outside of your home except for where you have a specific purpose, or a ‘reasonable excuse’
> If you live in a tier 4 area, you must stay at home. You must not leave your home to travel unless for work, education or other legally permitted reasons
So when Boris says "should" I believe he means "must unless you are in one of the excluded categories".
https://www.gov.uk/guidance/tier-4-stay-at-home#stay-at-home