As a first year student at Reading Uni in 1994, this day in that year was one which sticks in my mind - less for the maths exam I dashed through (passing, thankfully!), and more for the intense thunderstorms which developed/moved north during the evening.
It was a reasonably classic deep southerly flow, perhaps a Spanish Plume:
During the previous evening, AcCas blossomed across the Reading sky as the EML drifted north - the 12Z Herstmonceux sounding from the 24th shows a pronounced EML. Modifying this with the Camborne 12Z 900-700hPa temperature profile (making a very broad assumption that the approaching upper trough from the west caused cooling via lifting above a capped boundary layer, across eastern areas, leading to a similar 900-700hPa profile to Camborne's) and using the max temps (29C) and approx dewpoints in the warm sector yields sizeable and deep CAPE. As the trough approached upper flow increased too, with enough shear for well organised multicell thunderstorms, and perhaps updraught rotation.
From my point of view, after finishing the exam I went back to my hall - after dinner, at around 6.30pm, a large, thick cirrus shield overspread the sky from the south. About an hour or so later a thunderstorm commenced, bringing frequent lightning, strong winds, and plenty of rain. It went on for a couple hours before moving away - it was a very impressive storm although I think the storms further east were even more intense.
Here is some BBC forecast footage:
And some YouTube footage from a chap in Great Baddow, Essex: