What counts as symptoms for the purposes of self isolating?

[Borka]

DS & I have both had positive PCR results. DS had a positive lft on Tuesday and before that we both had cold symptoms but not the 3 official symptoms.

Does the isolation period started from the day of the cold symptoms?

My DDs flatmates had Covid and she was told that isolation started from the day she had a positive LFT.

Thanks, have just had a call from test & trace who said that the isolation starts from when the cold symptoms started.