For those in the south trying to get away to start ex-eu(s) trips etc the two hilltop airfields in the south are often the best place to look.
Bristol might be a better option for today (19th). Current forecast there is no worse than 4KM of visibility up until about 2100 tonight then getting foggy overnight.
Luton is forecasting 8km most of the day but with a possibility of 300 m in freezing fog before about 9am.
The other low airfields:
Stansted is forecasting being out of the fog by 0900 but that is unlikely to be early enough to not disrupt the first arrivals and thus second wave departures.
Gatwick is in the mist already with freezing fog to come by about 0300 and remaining till 11 ish if lucky and the afternoon if not.
Birmingham might just stay out of the fog with 7km vis but equally may get 200 m till lunchtime.