Cervantes called for "blessings on him who invented sleep, the mantle that covers all human thoughts". That is all very nice, but the author of Don Quixote did not, it appears, pay enough attention to how sleep has been divvied out. Not to put too fine a point on it, there is a danger of a slumber divide emerging to add to all the other divides - from digital to wealth - that we have to contend with. A survey carried out by the Sleep Council has found big differences in the amount of sleep people get, depending on their profession. At the top are solicitors with an average of 7.8 hours sleep - and 20% of them actually get as much as ten hours a night. Enough said.

At the bottom end of the scale, the worst sleepers (apart from hospital doctors on call who get only 4.5 hours a night) are MPs. They manage a miserable average of 5.2 hours a night. Although this excludes cat naps taken during dull debates in the Commons in the afternoons, it is worrying that the nation's legislators may be taking decisions when they are unfit to do so. According to research done at the University of British Columbia, each hour of lost sleep at night is associated with a temporary loss of one IQ point. Dr Stanley Coren, author of the research, also claims that sleep deprivation has been a major factor in causing disasters, including the Columbia space shuttle tragedy in February 2003 and the Exxon Valdez oil spill in March 1989.

Although the Sleep Council (funded by the National Bed Federation) has a vested interest in promoting a good night's sleep - presumably we will wear out beds out more quickly if we spend more time in them - it also makes some important points. There is increasing evidence that fatigue, often associated with lack of sleep, is a cause of accidents and diminished performance among car drivers, train drivers, airline pilots and others. But how such findings can be translated into laws that would improve behaviour, and reduce accidents, is quite another matter. Legislating about what we do at night as well as during the day might be considered an extension of the nanny state that is just too intrusive.