It was warmer in this country in Roman times. What caused that, all those 4WD chariots?
Unlikely. Horse drawn vehicles aren't really a great contributor towards increased carbon emissions.
Temperature fluctuations over time are natural (and occasionally disastrous) phenomena. The slight possible temperature increase you refer to was probably caused by a shift in the propensity of the gulf stream, which greatly impacts the climate of Britain. We are vulnerable to its whims. Hopefully it doesn't collapse as a result of climate change directly attributable to human activity as some scientists project, otherwise you're gonna need your winter fuel allowance back, and then some.