Hello Iwan
Assuming you have two or more coaxial cables starting in the loft and ending on wall plates in the lounge.
You could short one of the outlets in the lounge by putting a piece of wire beetween the inner and outer connectors, then go to the loft and try to pass a small current through each cable.
The one which returns the current to you is the one you shorted.
Hope this makes sense - if not come back.
Regards
W. Hole
