In terms of the frequency of updates the NATS/AIS AES tool is continuously updated (the office in the control tower at Heathrow is manned H24) and so provides a definitive source of information.
A few months ago a standby solution was negotiated by
Mike,
Rustle and the gang and is now supplied by NATS/AIS. This is useful on the occasions when the AES tool experiences a problem. This can be found
here and also from the login page of the NATS/AIS AES tool. Click the link called "Pre-Prepared Link (Contingency Measure)" and it will take you to the same page as the link above.
This contingency measure is updated twice a day and is broken down into 4 briefs:
London FIR & Aerodrome IFR/VFR Briefing
Scottish FIR & Aerodrome IFR/VFR Briefing
London FIR IFR/VFR Briefing
Scottish FIR IFR/VFR Briefing
The validity times are stated on the briefs. This only means that at the time the snapshot of the ADIMS database was taken say 14:00hrs these were the NOTAM that were in the database. The further time moves on from that initial 14:00hrs the more out of date the briefs become, so perhaps a little caution required.
I have heard of one pilot who, on approaching an aerodrome in the South East, was advised it was closed for a short period, due staffing. When he asked about it he was reminded that it had been subject to NOTAM action very recently. The upshot was that this NOTAM message was not included in his PIB from the night before so he missed it. He had to divert to another airfield.
I should explain the abbreviations........
ADIMS is the database where all the information resides.
AES is the portal which we use on the internet to access the
ADIMS database.