shows the values, dates and locations of the places recording the highest temperature in Britain each year from 1900 onwards to 2012 so far. In 65 years from 1900 to 2011, the temperature has reached or exceeded 32.2 deg. C. (c. 90 deg. F.), equalling 32.2 deg. C. in 12 of these years and exceeding 32.2 deg. C. in 53. The relative frequency of 32.2 deg. C. can be explained by the fact that until I think sometime in the 1960s, extremes, although usually read to the nearest 0.1 deg. Fahrenheit, were usually given given to the nearest whole degree Fahrenheit, so this could represent anything from 89.5 deg. F. (c. 32.0 deg. C.) to 90.4 deg. F. (c. 32.4 deg. C.). 32.1 deg. C. was also recorded in 1973 and 1991 and 32.0 deg. C. in 1986, these presumably being read to the nearest 0.1 deg. C.
By grouping these into occurrence by whole decades, we find that the number of such years in a decade varies from 2 in the 1980s (1983 and 1989) and 3 in the 1970s (1970, 1975 and 1976, though 1973 was only just behind with 32.1 deg. C.) to 9 in the 1940s (all years from 1940-1949, except 1946). There were also 8 years in the 1920s (all years except 1920 and 1927), and 7 years in the 1910s (all years except 1910, 1913 and 1916), 1930s (all years except 1931, 1936 and 1938) and the 1990s (all years except 1991 which was just behind at 32.1 deg. C., 1992 and 1993). The overall average is about 6.5 per decade, approximately 2 years out of 3. The longest consecutive run of years to record 90 deg. F. or over was 10 from 1994 to 2003 (there were 12 out of 13 from 1994 to 2006), followed by 7 in a row from 1939 to 1945 and 6 in a row from 1921 to 1925, all inclusive. and the longest period not to reach this temperature was 5 successive years from 1984 to 1988, although 1986 was only just below the threshold at 32.0 deg. C. Only on one occasion did two years in succession both fail to reach 85 deg. C. or c. 29.4 deg. C., these being 1962 and 1963 (27.8 deg. C. and 28.9 deg. C. respectively) although 1980 and 1981 (29.4 deg. C. and 29.5 deg. C. respectively) came very close indeed to this.
Maximum temperatures in each year varied from 27.8 deg. C. in 1920 (at Raunds, Northants, on 17th June) and in 1962 (Writtle, Essex, on 3rd September) to 38.5 deg. C. in 2003 (Brogdale near Faversham, Kent, on 10th August; this is on the Met Office website as the highest official temperature in Britain, but some authorities discount this due to excessive shelter but accept 38.1 deg. C. at Kew, London, on the same date).
One could do further analysis such as the average temperature and the highest and lowest for each decade and compare these with the overall average, but it seems clear that overall the 1960s, 1970s and 1980s have been poorer for very high temperatures in Britain than other decades. Interestingly though, the longest consecutive spell of years in Northern Ireland with temperatures of 80 deg. F. (c. 26.7 deg. C.) or higher, which could more or else be regarded as the equivalent of 90 deg F. in Britain (actually probably an equivalent of slightly more such as 92 deg. F. or so), was during this period, 6 years from 1968 to 1973, and 9 years out of 10 from 1968 to 1977, with only 1974, whose maximum was I think 26.0 deg. C. around 21st June, failing to reach this figure. However apart from 1976 when 30.8 deg. C. was reached on 30th June and 1975 when 29.7 deg. C. was recorded on 3rd August, no very close approach was made to the official record Northern Ireland temperature of 30.8 deg. C. (recorded in June 1976 as above and also on 12th July 1983) during this time; I think the highest during the period otherwise is 28.0 deg. C. in mid-August 1973 with other years generally about 27 deg. C. or so. 1976 and I think also 1995 are I believe the only summers to record 80 deg. F. or higher in all 3 summer months in Northern Ireland and indeed it is fairly uncommon for this to happen in 2, although I think this also happened in 1989, perhaps 2006 and probably at least 1 or 2 others in the past.