Further to the question about the CB cloud over Kent which could be
seen from near Heathrow, what's the furthest that CBs at our latitudes
can be seen?

In 2001 I saw two CBs that were apparently hundreds of miles away. Over
the August bank holiday I saw a CB from the South Downs (South Harting
near Petersfield) on the northern horizon which didn't look too distant
(I guessed London) but apparently it was over Norfolk, 200-odd miles
away. IIRC the date was 25th August (Saturday).

Further still I saw a very distant CB on the southern horizon from the
New Forest, the same summer. I remember looking at a lightning chart
for that day and the nearest was apparently in the Rennes/Nantes area
of western France, even further, 200 to 300 miles south? The date was,
IIRC, 26th July (Thursday).

Both occasions were very hot, humid, and sunny with no clouds apart
from these very isolated CBs.

Nick