Dick Lovett wrote in
oups.com:

The temperature list was restricted to sites with an elevation below
500 m asl, but this enabled it to include places such as
Flash in Staffordshire at 463 m. However, apparently, there were too
many reported minima for individual days from such 'upland' sites
during June to September, so
it was decided to restrict the recorded lows to 10 day periods so that
such media questions as 'what is the lowest temperature recorded in
the middle of August' could still be answered.

Dick Lovett
Charlbury OXON Cotswolds.

That makes sense, I suppose. I'd still like to see the daily figures
available somewhere, though, and I'm sure the media would as well - since
newspapers also like "date records". Midsummer's Day or August Bank Holiday
spring to mind (okay, not a fixed date, but close).

--
Bewdley, Worcs. ~90m asl.