By law, all employees must receive a written 'statement of employment particulars' within two months of starting work:
http://www.direct.gov.uk/en/Employment/Employe es/EmploymentContractsAndConditions/DG_1002790 5
No employee should be required to work more than 48 hours per week unless he/she has voluntarily entered into a written agreement, with the employer, to work for longer:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029426
There is no limit to the number of hours which can be worked in a single day. However, there must be a minimum 11 hour interval between the completion of one day's duties and the start of the next. There should be either a weekly break of 24 hours without any work, or a fortnightly one of 48 hours:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029451
(As will be seen from those links, more stringent rules apply to workers under 18 years of age).
For further advice on relevant legislation, start here:
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/index.htm
Chris