737-NG First Officer - Hadn't used my QFI rating for over 6 years, last test was 7 years ago.
The CAA wrote back and said do at the descretion of an FI instructor, then a test.
Yes, you will have to do a seminar as well, these are about £500 with accomodation and only run every 2 months.
On the plus side, your QFI rating will be valid for 3 years. To renew you will have to do 2 of 3 things : Test, Seminar, or 100 hours instructing.
I am planning to renew mine later this month, seems plenty of part time QFI work around nowdays.
Good luck !