urrrgh! trishalishous we have just been through all that with dd.(she's 3.5yrs.) i feel your stinky pain.
once she was outta nappies i refused to go back, so it's just been a long hard road of trial and error and a few knickers biting the dust!
we tried doing the reward for potty/no accidents/ accidents but tried to go potty, coupled with taking something away when she had deliberate, lazy accidents. this in essence has kindof worked. and just to clarify, by 'taking things away' i mostly mean tv, because she would get distracted watching tv and just go because she didnt want to miss the program or because she was in lala land.so i would ban her from tv for the rest of the day, or whatever.
also i think what has worked is getting her to help clean it up (ie towels, scrubbing wee off carpet etc) so she knows and gets an appreciation for how much work it creates every time she has an accident.
also we've just had a lot of really big, long, repetitive talks with her about it with a few different approaches, such as:
a) she really is keen to go to school, so i told her that if she wants to go to school she needs to be able to got to the toilet like the other big kids, or they will not let her go, and also it will be embarrassing for her, other kids might tease etc.
b) she's very dignified, and once or twice due to a lot of accidents in a row, she was going through undies quicker than i could wash them and she ran out.she HATED having to wear anything without them( i put leggings on her and stayed at home. what does one do?) but she's been mortified of having to go without again, which has also helped a lot.
c)its a lot of work having to clean up accidents, isnt it?don't you think its better to do it in the potty so you (and mummy) don't have to clean it?
anyway, that's what has worked for us, but i think the main thing is just repitition, drumming it into them and not giving in to nappies. if they know they have nappies to fall back on they will use the opportunity.
all the best op, i hope you're back on track with it soon.