The maximum working hours for safety critical rail staff are determined by the provisions of the Hidden Report.
No safety critical rail employee may work more than 12 hours in a shift. The break between shifts must be a minimum of 12 hours. The number of successive days worked must not exceed 13. The number of hours worked in any one week must not exceed 72.
Otherwise the same rules as apply to other workers are applicable to the rail industry. Workers are entitled to a minimum break of 20 minutes in any shift which exceeds 6 hours. The allowance is neither 'scaled' nor 'cumulative'. i.e. Someone working a 12 hour shift is still only entitled to one 20 minute break.
The average number of hours worked each week (calculated over a 17 week period) should not exceed 48 unless the employee has voluntarily entered into an agreement with the employer.
Workers should either have 24 hours free of work each week or 48 hours free of work each fortnight.
The rules are different for workers under 18 years of age:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/index.htm
Chris