When you arrive in the UK, you will need to follow the UK’s self-isolation rules. If you arrive in the UK from the Common Travel Area (‘CTA’) (UK, Republic of Ireland, Bailiwick of Guernsey, Jersey and Isle of Man) you will not be required to self-isolate on arrival in the UK.
There is also a short list of exemptions for those who, due to their type of work or purpose of their visit, will not be required to self-isolate (regardless of the place that they have travelled from). This list can be found here.
More information on UK requirements to complete a Public Health Passenger Locator Form can be found at https://www.gov.uk/provide-journey-contact-details-before-travel-uk.