The slowdown toward the end of 2020 will be followed by a slump in output in the first quarter of 2021
If 1709 was the year of the Great Frost then economic historians will remember 2020 as the year of the Great Pandemic. Everything that has happened to output has been related to Covid-19.
Overall, the economy as measured by gross domestic product fell by 9.9% from its 2019 level, making it the biggest fall since modern records began. At least for now, because 1921 runs 2020 reasonably close as an economic horror show, and at this stage the Office for National Statistics is only giving its first growth estimates.