Yes, a doctor can write you off work, but most doctors can only do it if you or someone in your life is actually sick, and therefore this type of sick note advising of the time you are allowed to be off should only be considered in cases where it is actually required. There is also a provision of a Statutory Sick Pay in some places and to claim that you need to be an employee and have done some work for your employer and your illness should have been present for at least 4 days in a row, which can include non-working days.