Can't really help as mine is just starting reception. If you know the area where you are moving to, I would advise to contact the Local Education Authority and ask to speak to the Special Needs Department.
Our daughter did not have an IEP in the states (long story). However, I did contact the special needs department and mailed them information on her, as well as meeting with the head teacher, special needs coordinator, and her teacher at her primary school. We also have a follow up appointment with her consultant pediatrician at the end of Sept to assess how she is doing both medically and how she is adjusting to school.
Another suggestion would be to see if there is a UK group for those affected by Autism. I just googled Autism and came up with this site:
http://www.nas.org.uk/The UK group for the syndrome that my child has sent both me and her school good information. They also offered to visit the school personally and speak to them.
I hope this helps in some small way.