"Ron" wrote ...
Apologies for posting an off topic question but i figured that
someone here would know the answer to this.

a place like news:sci.electronics.misc is likely more appropriate.

I live in a small block of
flats which has wall mounted tv and fm radio sockets connecting to
aerials in the roof. Which cable is best to use. the main problem is i
have to run the cable up and over a patio door and i would like to use
as thin a cable as i can so i can use a thin trunking to hide the
cables.

You will have to make the tradeoff decision between cable size vs. loss.
Depends on what kinds of cable you have to choose from, your definition
of "thin", the signal strength coming out of the wall outlet, the
sensitivity
of your receiver, and how tolerant you are of noise.

Also, would running a power cable in the same trunking cause
problems ?

Usually not.