I was there on the day and the WX radar was RED for the whole departure / arrival area around BKY and downwind for 05 at STN. There was fork lightning clearly visible to the west, northwest and on finals for 05. In the end London stopped accepting departures on the CPT and BUZ SID's. Watching aircraft decend on TCAS through a 10 mile long red cell is "interesting" (appreciate TCAS isn't always accurate in azimuth - but they were following the usual procedure for 05). Watching some depart was even more interesting! It was MUCH better after about 35 mins (which is still quite a while by UK standards).
If it's forecasting CRAP (everywhere) - just carry the extra gas, that way your hand isn't forced into something you may regret.
If anyone has heard the CVR of the Delta (?) Tristar that attempted landing in a TS at Dallas - it quite sobering hearing the guy willing the aircraft to "lift!, lift!, lift!, lift!" Just before impact..........
AlphaFour