
Hi
I worked as a Health and Safety Manager before giving it all up to be a Stay at home Mum so I can help on this.
The legislation you need is the Working Time Regulations for breaks etc these state that if you work 6 uninterupted hours you are entiled to 20 mins break - this can be your lunch break though. It also sets down times between shifts etc.
If you are looking at the numbers of staff that need to be present at any one time there is no legislation that states this. A risk assessment will need to be done to comply with the Management of Health and Safety at Work Regulations (reg 4) to look at what risks there are etc. You can lone work there is no law against that but they would need to ensure they had procedures in place for emergencies and breaks etc.
If you need any more infor let me know - I am not sure if I answerd your question as it was a little vague sorry!
Love
Kath x