Are proprietors of bed and breakfasts, guest houses and indeed hotels classed as landlords and therefore legally obligated to get a CP12 Annual Gas Safety Certificate ? If they are classed as such but do not get a certificate, who is responsible for monitoring/enforcing such matters ?

If its anything like a normal AST tenancy it will be a legal requirement. I would hope guest houses do have to have the gas inspected.

I would beleive the enforcement is at a time when a problem occurs. The onus is likely to be on the owner of the property making sure they do have a valid gas safety cert and service.

Similar with monitoring - its not unless there is a problem or reported as not being done.

If you know of a problem then report it. Carbon monoxide is a killer.