The Central England Temperature record, also known as CET is a meteorological data set that which was first published by Professor Gordon Manley in 1953. This was updated and extended in 1974 and is recognized as the oldest such data set in the world and is often used as a guide to climate change.
The data set ranges from 1659 to now and is presently maintained and updated by Met Office via the Hadley Centre. The data is monthly between 1659 to 1772 after that date the data became daily. Prior to 1772 there was an issue with the data quality which isn’t really surprising and this was addressed by Manley by not using the data prior 1772.
For a period of time they were two sets the official one, Hadley and another CET series run by Philip Eden until his death in 2018. The reason for the 2nd set was that the recording locations had been altered and Philip felt that by using other stations closer tot he original stations he could keep the record closest to the original data used by Manley.
The data set is created by using the Maximum and Minimum temperature for each day. The data is processed and a daily tracker can be found here.
At the month end data is quality checked and final figure may actually adjusted up or down from the figure shown in the link above. The CET for the last ten years can be found here. The full data CET can be found here.
Further information can be found on this web page
Some people will notice that there is a difference between the monthly average recorded on this web site and those displayed on the Met Office web site. This is because Sheffield itself is just outside the CET region. The difference seems to be about -0.2C in summer to -0.8C degrees in Winter. Of course the difference can be smaller or larger depending on the weather at the time. If Sheffield sits under fog for several days for example the difference could much greater than 0.8C by the months end.