3 core and earth on a light fitting

[Always learnin]

Good evening.
My son in law has moved into a 5 year old house with a conservatory. There is a 3 core and earth lighting cable poked through from the house into the conservatory which has never been attached to a light fitting. There is only ONE switch serving this light NOT two.
My question is how do I wire this into a new metal light fitting?
Assuming the brown to be live and the earth being the obvious bare unsheathed strand, which is the neutral .....grey or black? And can I close off the unused (grey or black) with a terminal block?

Thank you in anticipation

 

[westward10]

Without a test to the cable conductors it is impossible to say from here.

 

[Always learnin]

Without a test to the cable conductors it is impossible to say from here.

I thought as much but thought I'd ask. I wonder if when I go there tomorrow I'd get a clue by looking at the light switch to see if the grey or black was connected to L1 or L2?

 

[westward10]

Maybe, is the cable coming from the ceiling. Is it live because if it is that isn't safe.

 

[Always learnin]

Maybe, is the cable coming from the ceiling. Is it live because if it is that isn't safe.

When the wall switch is on, only the brown coming from the ceiling is live. Grey and black coming from the ceiling are not live with the switch on or off.

 

[DPG]

Can't believe it's been left live like that!

 

[Always learnin]

Can't believe it's been left live like that!

I'd hasten to add that with the wall switch off, all cables at the ceiling in the conservatory are dead.
When the wall switch is on, only the brown cable at the ceiling is live and both grey and black cables at the ceiling are dead. I thought either the black or grey would be neutral but which?

 

[littlespark]

It’s impossible to say 100%
It should be grey… but saying that, it shouldn’t have been left like that.

5 year old house, I’m thinking there will be a neutral joint at the switch, so it’s easy to check…

Testing live with a proximity voltage detector or god forbid a neon screwdriver?

Most outside lights don’t require a 3 core.
I’m confused as to why it’s there.

 

[Always learnin]

It’s impossible to say 100%
It should be grey… but saying that, it shouldn’t have been left like that.

5 year old house, I’m thinking there will be a neutral joint at the switch, so it’s easy to check…

Testing live with a proximity voltage detector or god forbid a neon screwdriver?

Most outside lights don’t require a 3 core.
I’m confused as to why it’s there.

Thank you littlespark. We're playing safe with this one and have an electrician calling by to do a proper, safe job with the right equipment.

PS yes it was both a proximity detector AND a neon screwdriver. Eeeek