One of the two main definitions of recession in the UK is at least two quarters of shrinking gross domestic product (GDP), the broadest measure of economic prosperity. Judged by this yardstick, the UK was last in recession in 2008-09, when there were six consecutive quarters of negative growth.

The economic shock triggered by the coronavirus pandemic caused GDP to fall by 2.2% in the first quarter of 2020 and by 20.4% in the second – the sharpest decline since modern records began in 1955.

Some economists believe this definition of recession is flawed, since an economy would not be in recession if it contracted by 5% in the first quarter, expanded by 0.1% in each of the following two quarters and then contracted again by 5% in the fourth quarter. It would, however, be deemed to be in recession if it grew by 5% in each of the first and fourth quarters but contracted by 0.1% in each of the second and third quarters.

An alternative – and tougher definition – is a full calendar year of negative output. Given the UK economy has grown on average by 2.5% over many decades, it is rare for gross domestic product (GDP) to fall on an annual basis. There have been only five such years since the end of the second world war: 1974, 1975, 1980, 1981 and 1991.

The US has its own method of assessing recession, with the National Bureau of Economic Research's business cycle-dating committee making a judgment.

The NBER defines recession as "a significant decline in economic activity spread across the economy, lasting more than a few months, normally visible in real GDP, real income, employment, industrial production and wholesale-retail sales".