Cool Hand,
The information you have been given is rather out of date!
The ATPL privileges include PPL priviliges, so if one is valid, the other is. It is only the aircraft rating you are renewing.
To renew an expired SEP Class rating, all you have to do is pass the SEP Skill Test as indicated by Gone West. If it has expired by less than 5 years the examiner does it. Over 5 years it goes to Gatwick for signature.
All of the requirements for 5- 10 and 10 plus have gone, the same rules now apply however long it has expired.