HELP My 3 and half year old will not poo on the loo

[Barbara145]

My three and a half year old will not poo on the loo. He was potty trained at a very early age (like his older sister)but will not poo anywhere except in a nappy (unlike his sister). He doesn't wear a nappy at night and hasn't for over 12 months.

I have just spent the last 2 months telling him that the nappies are running out and we can't buy anymore. He understands this and promises to do it on the loo but wont.

Have 'run out' this weekend but he became so upset I thought it might have a lasting effect..! So we 'found' some..

He has never dirtied his pants and will not.

We've tried bribery of many levels and are now at the Argos catalogue stage and 'pick whatever you want'... we even got the car track he wanted and offered to open it on the loo while he did the biz..

He has offered to sit on it but claims 'it wont come out'.

He has never suffered from constipation and is blessed with a healthy appetite and good sleep, exercise etc.

Any help??