Whenever one person is employed by another a contract exists between them. (If you offer me a fiver to do your shopping, and I accept, we've both entered into a legally binding contract).
While employers are not required to provide employees with a 'written contract', per se, they MUST (by law) provide all employees with a 'written statement of employment particulars' within two months of the employee starting work for the employer.
http://www.direct.gov...dConditions/DG_175704
Further, no employee can be forced to work more than 48 hours per week, when averaged out over a 17-week period. However individual employees can opt out of that limit as long as they do so voluntarily and in writing.:
http://www.direct.gov...ndTimeOff/DG_10029426
Working 12 days in a row is legally permitted but it would have to be followed by two days of rest. (Employees must either have a minimum of one day in seven off, or two consecutive days in fourteen):
http://www.direct.gov...ndTimeOff/DG_10029451
ACAS operate a help line, for employment issues, from 0800 to 2000 Monday to Friday, and from 0900 to 1300 on Saturday. Telephone 08457 47 47 47.
Chris