Ceiling wiring - how to connect brown and blue wires

[honestworker]

I disconnected a plastic spotlight (no earth wire or earth terminal) from the wires coming out of the ceiling without noting how the blue & brown wires were connected to the ceiling (my mistake - I have always connected to a ceiling rose before). The house was built about 1978. The attached photograph shows the wires coming out of the ceiling. 1) To where are the blue & brown wires on the spotlight connected on the terminal block with the black&grey wires? 2) Why is one of the wires coloured grey? (Is this loop wiring?)
All replies appreciated. Thank you in advance.

 

[FrodoOne]

Since all the several "Red" insulated wires are joined together (with another wire)
and
two "Black" insulated wires are joined together (with another wire) at the terminal strip,
the single "Black" insulated wire in the terminal strip must be the "Switched Line"
from the Switch
and should be "marked" to indicate this.
(Of course, you can check this by measuring the voltage between the "Red" insulated wires and the 2-Plus-1 ("Neutral) group in the terminal strip,
That mess of "insulation" around that which should be a "terminal strip" is unnecessary.)

Brown to the "Switched Line" wire
Blue to the 2-Plus-1 "Neutrals"

Why is one of the wires coloured grey?

Who knows?

(Is this loop wiring?)

No.

The wire connected to the "Red" wires (which might be insulated Brown?) and the Grey wire may go via a "cable" (which cannot be seen in the photo)
to another Light Point,
added after the original wiring.

If you disconnect one or both of them,
you will probably find that "something" is no longer working,
which will be to where those wires are going!

 

[sparkwright]

I disconnected a plastic spotlight (no earth wire or earth terminal) from the wires coming out of the ceiling without noting how the blue & brown wires were connected to the ceiling (my mistake - I have always connected to a ceiling rose before). The house was built about 1978. The attached photograph shows the wires coming out of the ceiling. 1) To where are the blue & brown wires on the spotlight connected on the terminal block with the black&grey wires? 2) Why is one of the wires coloured grey? (Is this loop wiring?)
All replies appreciated. Thank you in advance.

Yes, this IS loop wiring. Loop-in at the rose. One of the wires is grey because a newer cable containing brown, black and grey wires has been added. Grey has been used as a neutral - nothing whatsoever wrong with that.
It is quite possible the black in this newer cable isn't using it's black wire - again, that is ok - and shouldn't be altered.

 

[Taylortwocities]

Looks like the newer additional cable may be feeding something like a fan?

I guess the new cable is brown, black and grey? Would be good to see a wider view so we can see which wires come from which cable.

Without testing, I guess you do as @FrodoOne has suggested. Note: that conglomeration of connectors cannot just be shoved back in the ceiling. They should be all nice and cozy inside an enclosure or use a proper junction box.