In UK Black & Red feeds from the ceoiling rose.
I am installing a new fixture which has three transparent sheaths and one earth,
Fixture cables one appears blue one other brown and one seems to be bi-coloured white & blue.
I have tried different options and can get a trip or am left with the light continuously one.
I have brown to red & blue to black with the light on and will label wires 12or3 and table results...

Im From the UK also

Black and blue wires ate neutral wires
Red and brown wires are the live wires

You said you have a celing rose... in the ceiling rose how many wires are connected in it?

The light being continually on is because your connecting the always live(loop wire) directly into the live terminal therefor by-passing the switch

If you could maybe take a picture and send it to me I could mark out where everything goes