Here are the maximum UK temperatures for each day in September. There is currently an issue with the uploaded Daily Weather Summary at the Met Office Digital Library which means the data is only shown up to 22 September at present. I have flagged this with the library but in the meantime they have provided me with a copy of the full file. So here is the data.
We did have one date record this month (highlighted in red) on the 22nd. In fact the date record for the 22nd was easily the lowest of the month so was a bit of an anomaly. Despite breaking the record by 1.4C this year the 22nd remains the lowest maximum date record in September.
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