Switch wiring for lights and extractor fan

[Stephen74]

Hi all, I did train as an electrician but never worked as one so my experience is limited and ive not done anything for a while now.
I have an extractor fan in my kitchen that comes on with the lights and its damn annoying. I did disconnect it a few years ago but on a recent inspection the landlords electrician reconnected it. Its LOUD. Can be heard through the walls and can be heard in other peoples flats (and i can hear theirs)
The light switch is has two switches on it, so I thought why not simply put the fan on the spare switch? Opened the switch up and was met with the following.
2 cables going in to the box. The left has a red and a black wire (and the earth is folded over on itself) , the right has a red, yellow and blue wire.
3 terminals on each switch. 1 at the top, 2 at the bottom.
Left side switch has a single red wire going from the top terminal to the top terminal on the right switch. There are no other wires in the left switch at all.
Right side terminal has 2 red wires going in to the top terminal, a red and a yellow wire going in to the right side bottom terminal, nothing in the left side terminal.
The black and the blue wires are sitting off to the side in a choc bloc.

What the hell is going on?
My best guess is the connecting red wire is irrelevent.
The cable with red, yellow and blue is for the lighting and the cable with the red and black is for the fan, its a bit high up for me to check right now.
But from there I am at a lose as to why they've done what they've done.

- Ahh, im assuming they've done this to share power...

 

[SJD]

At a guess, the 3-core cable has L (red), switched L (yellow) and N (blue) while the T&E cable has switched L (red) and N (black).
If you separate the red & yellow (currently in one terminal of one switch) into separate switches, likely the light and the fan will now be switched separately. Obviously with the power off, and safe isolation. I have the impression they were originally switched separately.

Edited to what I meant to say (in red). Though Brian's post below may instead be correct.

 

[brianmoooore]

At a guess, the 3-core cable has L (red), switched L (yellow) and N (blue) while the T&E cable has L (red) and N (black).
If you separate the red & yellow (currently in one terminal of one switch) into separate switches, likely the light and the fan will now be switched separately. Obviously with the power off, and safe isolation. I have the impression they were originally switched separately.

Surely both red and yellow of the 3 core are switched lives. One to the fan and one to the lamp.
Agree that is has been changed to a single switch from a switch for each.
Looks like they didn't bother to tighten the terminal screw after they removed the wire, it has dropped out, and is now lying in the bottom of the metal box.

 

[Stephen74]

Yeah, once I realised they had done blue to black to get power it all made sense and i just moved one of the wires over the other switch and it was all good. Weird how not seeing one little detail straight off can throw you like that.