Boris Johnson says the public must not let businesses down when they reopen on Saturday.
Bricks and other missiles were thrown as officers tried to disperse the gathering in west London.
Portuguese leaders say the country's exclusion from a list drawn up by the UK government is "absurd".
Landmarks will be lit up blue ahead of a nationwide clap to celebrate 72 years of the health service.
Lockdown measures in Wales are still in force as pubs open in England on Saturday.