Bit of a mess, JJ.
That socket is totally out of order. The fact that you have go under the stairs and change the fuse in the consumer unit, suggests that this is wired on the lighting circuit.
5-Amp sockets for lighting and light loads should look like this.........
https://www.screwfix.com/p/mk-logic-plus-5a-1-gang-unswitched-round-pin-plug-socket-white/11412
(Used with a 5 Amp round pin plug.)
Anyway.. I don't like this the way it is. (Quite safe... don't worry...... it's just obviously wrong.
While I'm wagging the finger.......... recommended intervals for testing electrical installations should be 10 years for domestic properties.
Do have a complete check-up done on the whole thing........ preferably replacing the old re-wireable consumer unit with a modern one at the same time.
You need a "proper" electrician JJ :o)))