Customs Commissioners (C-520/06) (2009) All ER (EC) 906 and Pereda v Madrid Movilidad SA (C-277/08) (2009) ECR I-8405 followed. Night work Where a person works at night, they may only do 12 hours in any 24-hour period on average, or simply 12 hours at most is dangerous. It can be called a night shift. Breaks Every worker must receive at least 11 consecutive hours of rest in a 24-hour period, and in every day workers must have at least a 20-minute break in any 6-hour period.<ref>Commission v United Kingdom (2006) C-484/04, [2006] IRLR 888 held the employer is under an obligation to ensure the breaks are actually observed.</ref> 48 hour working week The most controversial and widely known provisions in the working time laws, however, concern the maximum working week. Under the Directive, this is 48 hours. Although people in the United Kingdom work the longest hours on average in Europe, and among the longest in the developed world, highest work related stress and absentee rates, successive UK governments have remained sceptical about the maximum working week's merit. The maximum does not apply to anyone who is self-employed or who can set their own hours of work, as it is aimed to protect workers who possess less bargaining power and autonomy over the way they do their jobs. Nevertheless, all UK workers may "opt out" of the 48-hour week by individually signing an opt out form. Theoretically a worker may always change her mind after having opted out, without suffering any detriment. If the employer has not got the worker to opt out, then the 48-hour week is not a rigid maximum, but is taken as an average over 17 weeks. The same rules have developed as for the minimum wage, regarding "on call" time, so that people with jobs involving long periods where they must make themselves available, but not necessarily be active, are regarded as working if they are bound to remain awake and close to their workplace. This created a significant problem for junior doctors, where the culture has typically been in all European countries that very long hours are expected. The European Court of Justice's decision in Landeshauptstadt Kiel v Jaegar'' that junior doctors' on call time was working time led a number of countries to exercise the same "opt out" derogation as the UK, albeit limited to medical practice. The Health and Safety Executive is