What can cause a plug pin to look melted?

I have had a few to drink and sleeping downstairs as my mate is in my room. I accidently pluged out the downstairs computer to plug in my laptop and as I did it I discovered a pin is slightly black and looks a tiny bit melted, hopefully I will get a picture tomorrow.

The plastic plug looks fine, it is just the pin that looks damaged (it is not old) but we have a 60w lamp, the computer and answerphone all plucked into a 3 way adapter.

Sometimes I have two PCs connect to the PC circuit via a KVM so could be that is being overloaded and the 13amp fuse is not blowing?

Converting the single socket into a double is not an option as there is no slack in the cable I don't want to touch it.

We can't afford any PIR checks done . Would it be a good idea to buy a heavy duty 4 way extension lead and fit it with a 5 amp fuse? I've seen it before with 13amp adapters not blowing the fuse even though its heavily over loaded.

Ok tomorrow I will buy a 4 way adapter and fit a 5 amp fuse to it, then if there is any problem with overloading it will just blow the fuse before potentialy melting a plug.

Your won’t be overloading the circuit with what you have plugged into it; sounds more like there is a problem with the wiring inside the box or the socket outlet unit itself.

A small burnt spot on a plug pin may just be the result of removing a plug with the load still connected, causing a small spark. A quick rub with a thumb usually removes the evidence.

However, a worn socket or plug can result in a high resistance connection which usually gets worse. The connection overheats, so the socket contacts oxidise and deform, so the contact resistance increases, so it overheats more etc, etc.
If a plug pin is discoloured, or there are signs of melting on the plastic covering the base of the pins, this is likely to be the case.

Loose connections inside the socket can also lead to similar problems, oxidising the wires and contacts, and burning the cable insulation. If this has happend, then the conductors will need to be trimmed back to sound cable before replacing the socket.

It is unlikely the load is too high for the socket, but computer power supplies tend to draw a high initial start-up current, which may pop a lower value plug top fuse, even if it appears to be sufficient for the load. Computer internal fuses usually have a time delay characteristic to overcome the problem.

The weight of 3-way adaptors and the leads from them may put a mechanical load on the socket the design had not anticipated, which could initiate problems.

I would consider replacing the socket and using a good quality 4-way board on a short trailing lead.

Sorted it now, just replaced the adapter, the socket is fairly new. It was very loose so I have replaced it with a 13 amp 4 way block.