A. There is no mark for an ‘unofficial’ (or ‘illegal’) exclusion.
You can only ‘send a child home’ for the remainder of the same day, using Code C (with suitable provision agreed for their safety). After that, you must formally impose an exclusion: that can only be for a fixed period, or permanently. It cannot be open-ended pending some action by the parent.
Once an exclusion period is over, the pupil must be allowed to return. Remember, too, that full-time alternative provision must be made by the sixth day of any continuous period of exclusion. These are all authorised absences for which parents cannot be held legally liable.