Philip Eden replied...

I'm pretty sure that
the 1983 "mistake" in the MWR resulted in them publishing the 09-21 min
as the 12-hour min, which obviously will give much higher values.

Looking at the figures again I see you are right - but the 'correction' printed
in the 1983 issue simply says that 'table 10 for 1982 and 1983 summaries
continued with the former procedure', i.e. the night-time 12 hours not the
daytime hours. I did not realise that the reason for the correction itself
needed a correction!

I also
think the chance of missing a high night min in summer because of the 09-09
period is significantly smaller than one in three. The August 1990 Brighton
figure is accepted as the UK record before this year.

The heat caused me to get carried away ! Thanks for confirming that.

Julian Mayes, W Molesey, Surrey.