At common law an employer is under a duty to take reasonable care for the health and safety of his employees, it is not against any regulation for you to be there on your own but the standard of care is “the care which an ordinary prudent employer would take in all the circumstances”. Under the working time regulations, which you may have opted out of, but can opt back into, you are entitled to a minimum of 20 minutes break if the working day is six hours or more.
Take up your concerns with your employer; raise a grievance, if you feel strongly over your position. If you have been employed for one year or more you are entitled to go to an employment tribunal if you are dismissed, but I note you need the money/job.