If you are not sure, you can extend your visa on arrival at the airport. When you show your passport just say I want to extend my visa, and you will be directed where to go.
Really? Its that simple? Have you done this yourself, what is the process? If it's easy I might do it just to be on the safe side.
On a side note...do people think that Brexit will make it any easier/harder for us to bring our wives over or allow them to stay etc.