Work stress makes millions miserable during the day.

Workers at industrial units in Wigan, office space in Letchworth and workshop space in Stockport are likely to wake up happy, endure a miserable day, and then pick up when they get home.

According to a study which analysed the Twitter posts of 2.4 million people in 84 countries, the most positive tweets generally come in the morning and after work.

A computer program was used to search for words associated with positive and negative moods, with the results showing that mid-morning is the most miserable point of the day, with people peaking around midnight.

Researcher Scott Golder said the pattern is probably due to the effects of sleep, and in particular "Circadian rhythms", the internal "24-hour clock" that tells us when to sleep.

Sociology professor Michael Macy, from Cornell University in New York, said the results highlight the "refreshing power" of sleep but also show how work stress can dampen the spirits.

British workers were recently named in the top ten counties with the most office bugbears, citing complaining colleagues as their main cause of frustration.