I think that the properly designed, (reputable) ones contain miniature non-replaceable overcurrent and thermal fuses, on the basis that if they fail they are just discarded. There would be no purpose served by providing an accessible fuse. I wouldn't dispute that there may be unsafe non-compliant ones around.
The good quality units used here do indeed incorporate a one-shot thermal overload on the primary side. There have been concerns in recent years about some cheap imported units which have no protection though.
Like DJK, I've also seen 2 and 5A BS546 used for 12V DC on boats and RVs. Most new installations use a specific 12V connector though, with two small, flat blades both set at a slightly outward angle from vertical to provide polarization.
