I am not going to advise Sam as to whether he should or should not enter the system, but I am going to offer general advice to anyone venturing into the Bath stone mines.
1. A responsible person on the surface must agree to call out rescue if the group fails to return after an allotted time.
2. Every member of the group should have a helmet and an adequate functioning light. Spare lights and batteries should be taken.
3. Do not under any circumstances venture into the mine without a survey (map) and compass.
4. The survey should be used continuously to monitor the groups position - so that you always know exactly where you are. If you are already lost the map won't help.
5. Do not deface the walls by drawing arrows or any other graffiti.
6. Many areas of the mine show evidence of past collapse or imminent collapse. Great care must be taken in areas of collapse or instability.
7. Take litter and rubbish home with you - don't leave it underground.
8. Don't disturb sleeping bats.
9. Don't remove any original artifacts.
I think that covers most things.
As for a guide - be aware that nobody can legally provide a commercial guiding service in Box mines unless they are a qualified mining engineer. The system is excluded from the BCA scheme for cave and mine leadership. To operate a commercial enterprise in Box contravenes the Mines and Quarries Act unless, as previously stated, the operator is a qualified mining engineer.