There is no general rule as to who owns which fence. It all comes down to the way the land and boundary lines were split by the vendor when the properties were originally built. Each boundary should be shown in the deeds of the property. To find out which fences you are responsible for, check your deeds and see how they are allocated. If the fence line is marked with a ‘T’ on your side of the fence line, then this means it is your responsibility.
Sometimes the responsibility for boundary lines is not shown. In this case you would need to refer to the Seller’s Property Information Form, where the information should have been given when you purchased the property. Or contact the Land Registry Office for clarification.