This is probably just down to the door casing or lining not being plumb and so the weight of the door naturally makes it want to 'fall' open.
There's no great way to fix it to be honest, you could move the bottom hinge away from the rebate in an attempt to bring the door back in to plumb, the down side to this will be that the door won't close properly on the latch side. this could be remedied if you have linings by removing the rebate laths so that they fit the door again.
You could always fit a concealed door closer, I just put something behind mine to stop them from opening when not latched.
Hope this helps.
Upper hinge sitting out of line to bottom hinge will cause it to swing,[sometimes hinge just loosening ] aligning them should fix problem , you can always change them to rising butt hinges which encourages closing.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local