The left outlet can accept either 5 or 15 amp BS-546 plugs.
Sorry Sven, but the dimensions aren't right for that, and the 15A BS546 plug has a much larger earth pin than the 5A.
This outlet looks like the type designed to accept a 3-pin 5A BS546 plug, or the 2-pin 5A version (the latter has the line/neutral pins slightly closer together than it's 3-pin variant).
I have a couple of old BS546 adapters that have the same arrangement.
