The frontal surfaces bracketing the warm sector slope upward, away to the west in the case of the approaching cold front to the W, and to the east in the case of the retreating warm front to the E. Each of these surfaces can be associated with an inversion of the temperature profile. For example the approaching cold front intrudes a wedge of colder air at low level and the warmer air of the warm sector will be advected over the top of it.
A small low-level inversion was present at Herstmonceux (E. Sussex). Tony Pallot advises that the weak warm front sloping E into Belgium was probably responsible for this. But the line of the front was over 100nmi E of the sighting area, whilst the cold front sloping to the W was still too far west to be responsible for a similar small inversion on the profile at Camborne (Cornwall), which is itself about 115nmi W of the sighting area 1 We are advised that the Camborne inversion was probably a local stratification caused by sea-cooled air streaming over the Cornwall peninsula (email from Tony Pallot to Martin Shough, 26.07.07), causing a thick mist as revealed in RH nudging 100% throughout the first few thousand feet.. A frontal inversion appears to be ruled out.