Unless employees are required to operate machinery, or drive vehicles in the course of their employment, outright bans of this nature are often viewed as being harsh. Indeed as a young lawyer I was once advised that if you go out for lunch with a client and they order an alcoholic drink you should follow suit as it was considered rude to let them drink alone. Perhaps it was the legal initiation equivalent of being sent for "skyhooks" or "a long stand" but it is a principle I have strictly observed over the last 17 years!
Typically a policy on alcohol use during employment would say something like:
The fact Lloyds have imposed a complete ban suggests they aren't confident this type of approach will work with some of its employees. In fairness when half of your disciplinary and grievance cases in the last two years have been alcohol related you can't really argue that the decision is unjustified.
Lloyd's of London angers staff with workday boozing ban