Cube shaped adaptor with 13A sockets and a 15A plug.
The difference is the plug - a round pin 15A type.
15 Amp 250 V
Made in Hong Kong
This adaptor would therefore allow appliances with more recent 13A BS1363 plugs to be used in a property with an older BS546 outlet.
15A outlets can still be purchased, and until recently were commonly used for theatre and stage lighting. However it would be extremely unusual to find such an outlet in a modern home.
This fuse is the original Lyvia branded one.
The red holder is just a moulded piece of plastic - the actual contacts are in the adaptor itself.