Many thanks, Martin, Mike and Philip for kicking off the thread and
for the posts above.

Including the comments/observations already noted, and a few of my own
from an hour delving through Ogimet’s excellent SDB, here’s where I
reckon we stand:
Observations at or above 1041 mbar (the existing Br Isles September
record is 1041.2 mbar back in 1986)

ACCEPTED
1041.3 03980 Malin Head 11/00z * New British Isles September record
MSLP *
1041.2 03162 Eskdalemuir 11/01z to 02z High altitude 242 m
1041.2 03911 Lough Fea (AWS) 11/01z Altitude 225 m, may be slightly
high
1041.2 03105 Islay, Port Ellen (AWS) 11/01z
1041.1 03155 Drumalbin (AWS) 11/01z Altitude 245 m, may be slightly
high
1041.1 03904 Castlederg 11/02z
1041.0 03903 St Angelo 10/23z to 11/02z

I have REJECTED the following observations for the reasons shown:
1042.0 03047 Tulloch Bridge (AWS) 11/00z - REJECTED
Agree with all above comments, looks a mite high, high altitude (237
m) MSL correction (around 23 mbar) the probable reason
1041.5 03916 Ballypatrick Forest (AWS) 11/01z - REJECTED
Agree with comments above, does look a shade too high with near
neighbours. Also high altitude correction (156 m) close to 15 mbar
1041.3 03225 Shap (AWS) 11/00z REJECTED
Looks high with near neighbours. Again AWS at high altitude (249 m)
with ~ 24 mbar correction

So the September monthly record (has been beaten – but by the
narrowest possible margin. It also looks as though the altitude
correction on high-level AWSs may be a little over-done at high
pressures.

If anyone knows of any additional observations above 1041 mbar that I
may have missed, or perhaps observations between reported synoptic
hours, I’d be grateful for the information.

I must also make a correction to my post of yesterday evening, where I
stated:
I am prepared to be corrected, but I'm 99% sure it's the earliest '1040' on record in the British Isles - the August record (the lowest of any month) is 1036.7 mbar, and we're only 10 days into September of course.

Slap my wrists for relying on my failing memory instead of checking my
events database properly. Philip pointed out to me, quite rightly,
that I’d omitted an even earlier ‘1040’ just five years ago - I quote
from Philip’s monthly summary for September 2004:

“High pressure lay over southern Britain from the start of the month,
extending to all parts of the UK from the 5th-9th and the barometer
climbed to 1040.6 mbar early on the 7th at Inverbervie,
Kincardineshire (a new UK record for the first half of September).”

Thanks Philip – you’re right, I had forgotten that one! Thanks for
setting the record straight.

--
Stephen Burt
Stratfield Mortimer, Berkshire