This is the most of these that I've seen in the one place in decades.

Opinions will vary but, personally, I'd be dumping them:

https://i.ebayimg.com/images/g/LkMAAOSwIeZk78O0/s-l1600.jpg

A handful for display purposes, I'd do that but there is no way I'd put one back into service, even for myself. All it takes is one strand to come from under the screw and poke out to the side for a shock to occur. At the age these plugs are at, the bakelite is also too thin to run them through the normal rigours of daily use and it is prone to cracking. That will hurt if one is pushing a plug into a socket at the time the plug falls apart.

In most cases the cable is either unsheathed figure 8, or its cactus no matter what it is; plus the regulation, now banned, cable knot.

The biggest issue with the Bakelite (noted over 60 years) is its rigidity, related to shock, causing breakage and in certain circumstance the fingers can touch the screws, or prongs. That is likely the reason for the mandatory insulation on the newer plug top prongs.

In the main most old sets here are transformer, so the cable is usually replaced here by a modern cloth covered suicide cable, or repurposed computer IEC cable after the IEC end is cut off. That results in a lead with a sealed plug top and a grounded chassis. With a grommet, etc meeting modern regulations for securing that cable.
One should note that if its a shielded transformer, it will put a charge onto the chassis. That has on the odd occasion caused hum. However, grounding the chassis gets rid of it.

What I consider dangerous, and wonder how they got into the country?

I have modified several Signal Generators and other transformer devices with metal cases and two wire mains cables, with the chassis and cabinet connected to that mains cable with a cap. There is always the risk, especially with old ones that the cap is not a proper line cap and could be on Active.

To me that is not intrinsically safe and really should have had a three wire mains cable when built.

Yes, these plug tops were outlawed in the fifties and should be busted up.

And then there are those old double adapters that reverse active and neutral on each outlet.

Matsushita Electric's first product was a power plug made of wood. 100 volts AC in Japan not quite so dangerous I suppose.

There are woods that have a high dielectric strength and were used with electric fencing. One of my units is around 7KV.

Blackbean is an oily timber with a high electrical resistance.

Well I guess they must have been safe and no-one got killed because the company went on to be the behemoth we know today.
But life was cheap in those days LOL