DS is 4 next week and is still having multiple accidents a day.. HELP?!

[Unipottimus]

We have been potty training him for 20 months now! He decided at the beginning he didn't want to wear nappies anymore and went straight to the potty with very few accidents. 3 months later his little brother rocked up and that was the end of it. Some days he'd have up to 9 accidents. I foolishly refused to go back to nappies (I now think we could have just tried again at a later date but at the time saw it as a backwards step).

Lately he's been better, we even had a 4 day streak in the last week with no accidents (Kinder egg bribes..) but then today he's had 3 wees and 2 poos in his pants. I've tried everything; reward charts, marble jar, bribes, being cross (unintentionally), potty dances, pointing out his friends who are all dry, calling Grandma to boast (and getting lots of praise back), taking him to 'try' on the hour every hour (he just sits on potty, says know walks away and pees himself) I just don't know what to do - I'm at my wits end. He starts school next week just after his birthday.

Does anyone have any suggestions I can try before he becomes obese from the treats?

[Unipottimus]

no*