@Mummyme87 the DfE says otherwise.. if an in-school LF test is positive no PCR required. They do tend to make up their own rules (until they are corrected by PHE!)
The problem is that in school tests are reported to NHS and they don't seem to have a system to "negate" the positive with a subsequent negative, even though the scientists agree the PCR is more reliable.. so T&T say you have to isolate (and your household) because their system says you are positive for 10 days after test even if there is then a negative..
They seem not to have thought ahead to this scenario - much like most DfE issued guidance really..