If you were granted temporary permission for 3 years i would er on caution applying retrospective
imo they are playing games.
If you can prove 10 years residential use , i would wait and see if they issue you with a enforcement notice
If they do you can appeal it
After 10 years its exempt re enforcement so you should get lawful development certificate
You also have the option of applying for planning permission as well, taking the decision out of the hands of the council.
Best place for good advise is
http://www.gardenlaw.co.uk/phpBB2/viewforum.php?f=9&sid=7a4f6ee1ef3b8fcfe13280f3645fccf5If you post give full details and let me know
Couple of guys on their are bees knees could save you a fortune
Helped my enforcement case and made council look like a YTS trainee, they had egg on their faces