Whether you hold the party on or off Company premises, Company rules and procedures still apply. You need to ensure that this is clearly communicated to staff prior to the event. If you are faced with a member of staff breaching your rules of conduct at the event then your normal disciplinary procedures would apply.
As an employer you need to think about how your employees will get home after the event. You have a duty of care to ensure that they do not drive home if they have been drinking, for example ensuring there are adequate alternative methods of transport available from the event such as late night buses and taxis. You would not be expected to pay for these but should ensure they are readily available.
If there is any damage to the venue by an employee, then as the organiser/ employer you may be liable to any costs associated as a result of the damage. However, this would be considered as misconduct and therefore your disciplinary rules would once again apply.
In summary, as an employer you have a duty of care to ensure the safety of your employees and can be liable for the conduct of your employees whilst at a Company event. Your employees have a duty to observe the Company rules and behave accordingly.
