Certainly makes one think,what would I have done if it did clag over,all we have is a radio and very few basic instruments,anyway I'm not trained IMC?
LN, as far as I know, if fog rolls in suddenly it's typically a very local effect and the fog layer is usually not that thick - maybe 100 feet at most. So you can usually divert above the fog layer to a fog-free airfield.
Obviously this is not true for fog under an inversion or related to a warm front. That sort of fog can cover large areas. But that type of fog typically doesn't appear in a matter of minutes, and is usually forecasted in any case.
Somebody with more experience in typical UK weather can comment further?