Jayne- i have the same problem, Madison when we are home will use her potty and have no accidents unless she is outside and forgets about it, I even took her out the other day with out a nappy on, but she did have an accident but she really did not like it. HOwever she sent the night at my mums house and had to be put back into nappies.
Also she will tell me when she has done a poo straight away, it is fustratimg as they know when they have to go but they refuse to.
Sorry i have no advice just wanted to let you know that you are not the only one out there having troubles