Poor you. Bumping for you as not much experience really. We had a week of regression recently with my DD but she had only been trained for a couple of months. Nothing obvious had changed as far as I could tell as to why it happened. She just started weeing all over the floor again (unfortunately we have yet to crack poos so i feel your immense pain!).
We went back to basics with stickers, enthusiastic praise etc for successes. I asked DD if she wanted to wear nappies again and she said no. In the end the thing that cracked it was that I said to her that mummy was sad that she was no longer weeing in her potty and she sat on it and did a wee there and then.
Am sure there are loads of people on here that can help as this is particularly frustrating I know x