Bottom line is that central London does have a UHI of about 1.5 deg C. This however doesn't change over the last 45 years. The rate of warming at all the London sites is the same. 1.5 is the average UHI, but it can be up to nearly 5 but as low as 0 on some days - see the distribution histograms.
Weekly Climate and Energy News Roundup #174
2 hours ago