I expect my wife will go to the USA soon and currently she is demanding our two children's Thai and UK passports....do i have to hand them over ?

I am in Nong Khai and there is a good chance the police will be called...will i have to hand them over ?

First, why are you not wanting to give the passports?

Are you attempting to make it so your wife and/or children may not leave the country? This is a bit grey but this may fall into theft and if a lawyer was really savvy, there are all kinds of other crimes that may be being committed depending on what you two have said to each other such as extortion or worse.

The passports are not yours and you have no right to deny the rightful owners custody of their own passports.

If it the police are involved you will lose !

The reason i want to keep the passports is because the last time i had a row with the Mrs..she left them with a Laos national in Thailand and went to USA for 3 mths...i had planned a trip to UK with my wife and 2 kids but felt helpless to do anything without the UK and Thai passports for my children.The UK embassy said the UK passports belong to the UK and my wife cannot hide them but in reality....how enforceable is that ? If i am the legal father surely i have as much rights as the mother concerning holding children's passports

This all sounds like a bad idea. I'm fairly certain that you can't with-hold something like passports from your family members.

While it may be a grey area and the UK may own the passports, you don't own them anymore than they do and you don't have a right to withhold them. I'm fairly certain you would lose if this went to court.

Give her the Thai passports. You keep the UK passports.