mick wrote:

It's 3-phase cable without a neutral.

brown = red = L1
grey = yellow = L2
black = blue = L3

If you are using it for a single phase+neutral supply then, strictly
speaking, it is the wrong stuff. It would be a pity to waste it, so I
would suggest that you use it as follows:

brown = live
black with blue sleeving = neutral
grey with green/yellow sleeving = earth

Note: you must sleeve the conductors at both ends.

You must also earth the armour (via a proper cable gland for wire armour,
but at 2.5mm2 I suspect that you have braided cable so cable entry is via
a stuffing gland and take the braiding to an earth terminal).

It's wire armour, and Wickes sells the glands
for that, on the shelf over the cable.

Thanks.