Climate scientists have said such heatwaves are becoming more frequent as a result of global warming from greenhouse gas emissions.
In a report published in the International Journal of Climatology, the Met Office extended its temperature records for Britain by 26 years back to 1884.
Analysing that data, it found that the warmest year on record in Britain was 2014; followed by 2006, 2011, 2007, 2017, 2003, 2018, 2004, 2002, and 2005.
"Looking back further into the UK's weather reveals a very interesting timeline with the top ten warmest years at the most recent end, since 2002," said Mark McCarthy, the head of the Met Office's National Climate Information Centre.
"Notably, 1892 is the coldest year in the series, when the average temperature was just over seven degrees. By contrast 2014, which was the warmest year in the series, saw an average temperature approaching 10 degrees Celsius," he added.
The top 10 coldest years in order were 1892, 1888, 1885, 1963, 1919, 1886, 1917, 1909, 1887, and 1962.
The report also said that although last year was the most significant snowfall since 2010, snow events have generally declined since the 1960s.
Over the past decade, summers have been 13% wetter and winters have been 12% wetter than in the period 1961-1990.
The average sea level around Britain was also the highest on record in 2015 and 2018 since records from 1901.
Commenting on the Met Office report, scientists said it was a sign of the "new normal".
"With global emissions of greenhouse gases on the rise, the UK will continue to get warmer and wetter as global warming accelerates. The science of climate change is now clear," said Michael Byrne, lecturer in Earth & Environmental Sciences, University of St Andrews.
Worldwide, average temperatures have risen 1 degree Celsius above pre-industrial levels since the mid-1800s.
Governments have agreed to limit temperature rises to within 2C this century but current emissions cut pledges are not enough and put the world on course for a 3-5C rise.