Is there any reliable information as to the current rating of a twin 13 amp socket.

Sounds simple enough, but views seem to differ. I was taught (decades ago) that a twin 13 amp socket manufactured to the relevant standards was suitable for a total load of 20 amps. And I recall that approval testing was done with 14 amps on one outlet and 6 amps on the other.

More recently though I recall respected members of this, and other forums, stating that the maximum total load is 13 amps and not 20 amps. And yes I know that 13 amp twin sockets  are marked “13 amps” on the back. But does this mean “maximum total load of 13 amps” or does it mean “intended to accept 13 amp plugs”

Any reliable views on this, preferably with a source.

And related to the above, I have heard that MK twin 13 amp sockets go beyond the minimum standards and are designed for a total loading of 26 amps. Can anyone confirm or deny this. And yes I have asked MK and have received several different answers !