Please see the information below from the Department for Education:
Changes to the self-isolation period for those who test positive for COVID-19
From Monday 17 January, people who are self-isolating with COVID-19 will have the option to reduce their isolation period after 5 full days if they test negative with a lateral flow device (LFD) test on both day 5 and day 6 and they do not have a temperature. For example, if they test negative on the morning of day 5 and the morning of day 6, they can return to their education or childcare setting immediately on day 6.
The first test must be taken no earlier than day 5 of the self-isolation period, and the second must be taken the following day. All test results should be reported to NHS Test and Trace.
If the result of either of their tests is positive, they should continue to self-isolate until they get negative results from two LFD tests on consecutive days or until they have completed 10 full days of self-isolation, whichever is earliest.
Anyone who is unable to take LFD tests or anyone who continues to have a temperature will need to complete the full 10 day period of self-isolation.
Further information on self-isolation for those with COVID-19 is available.