There has been no change in UK average temperatures in summer(JJA) or in Spring(MAM) for the last 367 years. The two hottest summers were 1826 (17.6C) and 1976(17.8C). I remember 1976 as the perfect summer with two months of continuous sunshine, causing a severe drought. The two coldest winters were 1740 (-0.73C) and 1963 (-0.07C). 1963 was the perfect time to be a small child aged 10, sledging every weekend. These extremes have not been exceeded for the last 40 years.
If you are looking for evidence of climate change in the UK then you will notice a possible small upturn of < 1C since 1950 during Autumn and Winter. This supports the argument made in the last post that any small increase in CO2 forcing mainly changes meridional heat transport during winter. It could also be due to the urban heating effect from buildings during winter months.
Here is the annual data. The one you see plotted say by Ed Hawkins is instead as temperature ‘anomalies’ relative to a 1961-1990 average. This is baseline is represented by the bottom red line.
On that basis you could argue that the UK has ‘warmed’ by 0.6 ± 0.4C since 1960. That increase is due to changes in autumn and winter temperatures.
Update: On request of Joe Public here is the comparison to CO2 levels in the atmosphere as measured at Mauna-Loa extrapolated back to 1750 (280 ppm)