I can provide additional letters for on and off register, as well as if parents refuse to place onto register once concerns are raised – email me if you need them: firstname.lastname@example.org
Just always make sure that parents have been spoken to before hand and that this is referenced in the letter eg “as you are already aware” or “following our conversations” etc. I would also recommend that you have a response slip from parents to acknowledge the letter and action that will be taken. Just makes sure that you have the evidence required should parents turn around at a later date and say they were not aware.
Hope this helps,