Since 2019 the U.K. Met Office has provided monthly observations, beginning in 1884, on maximum, minimum and mean monthly air temperatures for the U.K. and its regions. Time series analyses of these data are reported in this paper, using a deterministic monthly trends model. Although the U.K. has seen significant trend temperature increases between 1884 and 2021, these increases differ depending on whether maximum, minimum, or mean temperatures are being considered, with trend minimum temperature increases being greater than trend maximum temperature increases. There is also a difference in the trends exhibited by temperatures in the central and peripheral regions of the U.K., with rather larger trend increases being found in the former than in the latter. The largest trend increases are invariably found during the autumn months, usually October, while the smallest are found in June for maximum temperatures, which are usually insignificant, and in winter for minimum temperatures.