It comes down to local topography and the time of day. For example Gatwick is usually foggier at the western end due to the river Mole flowing through that part of tne airfield.Fog though is usually associated with light winds so an approach with a small tailwind should not be a problem unless you are going to overfly the local population and in an autoland we like to fly a stable draggy, noisy approach rather than the usual quiter decellerated type.
Birmingham has a number of berms built around the runway edges and there is a stream at the southern end which may trap the fog in certain parts.It will be interesting to see how the manmade topography affects the RVR..