I remember that storm well - it was the day we moved into our first flat. I remember the sky going a green colour before the storm too - it was certainly one of the most spectacular I've seen - especially as we were driving through the Essex countryside in the middle of it. Another spectacular storm I remember from my childhood in Essex was the "Dunmow Hailstorm" of 26th May 1985. Started with ~2cm hail, which increased in size over several tranches up to about tennis-ball size. Recorded in the TORRO database here: https://www.torro.org.uk/research/hail/events