@Okay
Your suggestion of going up on the roof might just be acceptable if you get an engineer who's willing to work with you. I would imagine you would be rquired to "tack" the cable to the wall as you go (under their supervision). Feed it through and then seal it.
You can but ask. Like removing the old copper overhead wires.
Engineers are not allowed to work in lofts unless they are floored, have easy access and space to work in. Apart from that several people on here have had a loft CSP fitted. Other's have pre-installed duct with a draw rope to pull the cable through and then hoped that the engineer was happy with the arrangement.
Brian
