All persons arriving in the UK must fill in a Passenger Locator Form before arrival.
Before departure to the UK check if any of the countries you have visited in the last 10 days are on the red list.
If you have visited a country on the red list you must follow the red list rules.
If you have not visited any countries on the red list, what you have to do depends on your vaccination status. Check the rules before you travel at gov.uk/coronavirus.
Failure to comply with these measures is a criminal offence and you could be fined. There are a limited set of exemptions from these measures. You may be fined if you fraudulently claim an exemption.