LG&T, I have just managed to read your post, what a tosser?
The way I see it you have two choices, either screw him for all he has, which as he says wouldn't be very much if he goes through with going on his own, and it would have an effect on the kids, or you take his offer.
It all depends really on the kids relationship with him, it sounds as though they are seeing him often and everything, is that what you want? Is he worth having in their livs if he won't do the right thing by them money wise? Or is he a better dad than what moeny he is offering? Would they miss him if he wan't in their lives as much?
If you agree to the £300, is he likely to keep paying it, or will he stop after a couple of months for one reason or another? In which case maybe the CSA is the answer because they can take it straight from his earnings so even if it would be a lesser amount, at least you would know it was coming in every month.
Is the £300 he is offering enough for you? If he is trustworthy enough to pay every month, is there anyway you could get him to agree to a higher amount?
As for pressing chargres against you for taking the things from your house, let him try, the police would laugh in his face!