Any adult who works up to, and including, 6 hours per day has no entitlement to any breaks
Any adult who works
more than 6 hours per day is entitled to a single (unpaid) 20 minute break.
That entitlement is not 'cumulative'. e.g. if someone works for 12 hours or 18 hours, they're still only entitled to a single 20 minute break.
A person who is over school-leaving age, but under 18, is entitled to a single (unpaid) 30 minute break if they work more than 4� hours at a time. (Once again, the entitlement is not cumulative).
There's no other entitlement to any other breaks (such as 'tea breaks').
In some circumstances, health and safety regulations might mean that a person has to be rested from a particular job more often (and/or for longer periods) than the above rules state. However, that doesn't give the worker any additional right to breaks, since the employer could simply take them off one type of job and assign them to another.
http://www.direct.gov.uk/en/Employment/Employe es/WorkingHoursAndTimeOff/DG_10029451
Chris