Roseformeplease - there are absolutely cases where a child is in school and the teachers are keeping a weather eye out without doing anything official, but there are informal safeguarding concerns. In such cases, the teachers ABSOLUTELY have a responsibility to refer the child to SS if (s)he is deregistered from school, since their safeguarding role is at an end.
But if there is no reason to suppose any welfare issue apart from the fact that the parents are deregistering, then the guidelines are absolutely clear that no referral to SS should be made.
Teaandalemontart - what unschoolers will provide to the LA varies.
Some will have meetings (but only where that LA official is known as understanding the principles of that approach).
The parents OFTEN send in an "educational philosophy" which is a couple of sides of A4 laying out their educational goals and principles.
It can often be problematic sending in any sort of educational "product", since, by its nature, the products of an informal education can be ephemeral (send in the sand pit in which your child did a heap of writing last week?!). Some people are also adamant that any educational "product" belongs to the person who produced it and, without permission from that person, they are not willing to let an LA person see it.
Personally, I always have a big supermarket carrier bag on the go in which I collect completed activity books/art works/ treasure hunt clues/ expired season tickets etc etc. I don't date any of it, or identify the child(ren) involved, because life is too short - I can work it out through a process of domestic archaeology if necessary. I also take photographs of a lot of the coolest stuff we do, and email them to myself so that if my phone is stolen it isn't all lost. For one of my children, a lot of their animations are preserved online, and there are a huge number of images created in microsoft paint which all get backed up every month or two. If we were ever taken to court, I would provide the court with many many bags and files of this stuff, and the LA could catalogue and sort it out themselves (there is case law precedent for precisely this approach as a successful way of demonstrating that an education is taking place to the satisfaction of the court).