The National Minimum Wage Act specifies the minimum rates of pay applicable nationwide. However, how much you are entitled to depends on how old you are.
As of 1 October 2009, the rate for people over 21 is £5.80 per hour. For 18 to 21 year olds, it is £4.83 per hour. This lower rate also applies to some trainees. Since 2004 there has also been a minimum wage rate for 16-17 year olds, currently £3.57 per hour.
For calculating what you're owed, 'pay' in this case means gross pay and includes items such as overtime, bonus payments, commission and tips and gratuities which are paid through the payroll.
There are special cases for some workers. For example, students doing higher education work placements are exempt. Those on standby or workers provided with accommodation have different regulations, and the minimum wage doesn’t apply at all to family members working in the family business, volunteers, or people working and living as part of a family.
For further advice, contact your union, see the National Minimum Wage site on the Directgov website, or ring the Government's National Minimum Wage helpline on 0845 6000 678 (charged at local rates).