Today's minimum MSL pressure here was 961.1 mbar at 1405z (value from
Fortin mercury barometer, backed up by PAB 961.2 mbar and Davis AWS
value of 960.9 mbar). This is the fourth-lowest value in southern
England west of London within the last 60 years (see details below).
It is still 9 mbar higher than the Feb 1989 event, which was the
lowest in London since 1821.

For southern England west of London, the only lower barometric
pressures since 1949 have been:

4 Feb 1951 - 960.8 mbar at 2100 GMT at Heathrow
The lowest pressure reported was at Midleton, Co. Cork (about 40 km
east of Cork) at 1500 GMT when the barometer stood at 942.3 mbar: this
is the lowest on record for February in the British Isles. Over the
whole of Wales and all parts of England south of 53-54°N the pressure
on this date was the lowest on record over the period 1949-88. At Kew
Observatory the minimum pressure on this occasion, 961.2 mbar, was the
lowest since 9 December 1886, when 958.7 mbar was recorded. Reference
1.

16 Oct 1987 - 958.5 mbar at 0400 GMT at Mortimer Common, Berkshire
The 'Great Storm'. The lowest land MSL pressure was 957.2 mbar at
Plymouth at 0100 GMT. The centre passed over Gloucestershire at
957-958 mbar. Heathrow's minimum was 961.6 mbar. Reference 2.

25 Feb 1989 - 952.1 mbar at 1730 GMT at Mortimer Common, Berkshire
Over Dorset the barometer fell below 949 mbar at 1500 GMT, while in
London the pressure fell to 952 mbar during the evening - the lowest
since December 1821. Heathrow's minimum was 952.3 mbar, Gatwick 951.5
mbar. Reference 3.

10 March 2008 - 961.1 mbar at 1405 GMT at Stratfield Mortimer, Berkshire. Heathrow's lowest MSLP from 3 hourly obs was 961.8 mbar (at 1450) and the 30 min TAFs show 962 mbar 1350-1520, so this is probably just about the minimum there - and therefore just short of the 1951 and 1987 values. It is a new March record, however, the previous LHR record for March being 968.9 mbar at 2100 GMT on 13 March 1951.

These are '24 hour' extremes based on Heathrow's hourly observations
1949-85 and my own observations in Berkshire since 1978 (mercury
barometer and calibrated barograph, and since 1993 5 min resolution
AWS data). They are not based upon 'once per day' (normally 0900 GMT)
readings only.

Reference 1: Weather, Jan 2007
Reference 2: Weather, March 1988
Reference 3: Weather, May 1989

--
Stephen Burt
Stratfield Mortimer, Berkshire