Adding outside light to existing outside light.

Hi.

I’ve currently got an outside light (pictures attached). It’s a 3 twin and Earth whereby the cable runs from a switch and the cable is in the wall and comes outside the brickwork into the junction box where the outside light is connected to it. The cables are all in the little white/clear connection blocks.
There are 2 neutrals which are in the same slot in a clear connection block however 1 of the neutrals is the grey cable from the house with a blue sleeve over.
The earths are all in the same slot on another block.
The permanent live is in another block on its own. Then the live from the outside light is connected to a block with the black cable from the house with a brown sleeve on so I’m guessing that’s only a switch live when the switch is in the ON position.

My question is can I wire up another light for the side of the house to this point and would it be to the single live or the switch live depending on if I want it to be switched on or off like the other existing light.

I have a bigger junction box and wago connectors, 20mm conduit piping for the T and E cable and the outside light. Would 1.5mm T and E cable be fine?

 

Thank you for the replies so far.
To clarify I already have conduit for the cable as I’d read the T and E isn’t UV and weather proof so I’ve gone for 20mm conduit.
I have a medium sides rectangular shaped junction box which has the rubber gasket seal between the box body and its lid. I was planning on putting silicon beading around the top, sides and entry from the house into the box to get a good seal as Persimmons haven’t done that when they installed it from new build.
So what cable would be best to connect them, 1 or 1.5mm as I have a reel of 2.5mm given to me. Also the cable Persimmons have installed looks to be 1.5mm if not thicker 3 core and earth.
Any advice on the best way to seal the pipe into the junction box for the tighter seal? I have 20mm closed grommets at the moment as my intention was to make a small nick into 1 to feed the cable from the light through and only use the conduit for the run of T and E between the existing light and the new one.

 

I’ve wired up the light and the cable end into the light but had to stop because of the drizzling rain here so I’ve tucked the exposed end of the cable into the end of the conduit for now until I can get back outside and strip the current junction and fit the new box, wire it all in and job done.
I’ve used the 2.5mm T and E at present as I wasn’t going to waste it and spend more on cable when you guys said it’d do.