Right, a bit of an update
I've spoken to Sky and they've said there's no problem with the pay £25 and remove the obligation for a phone line for non-multiroom. They also said there isn't a problem going for a chimney install as long as this is requested at the time of ordering (and he said I could always call them if any problems with doing this on the website).
With regards cabling, as others have said they won't do any internal drilling, etc. and they would normally just run the cable down the drainpipe from the roof, round the side of the house and drill through into the living room. He said if we'd already done the internal drilling and run a piece of string for them just to pull through that'd be fine (and less work for the installers). We've now been down under the house and found the relevant entry points at the bottom of the drainpipe and at the floor near the TV but I was wondering if it would be easier just to run the cable ourselves - i.e., to go out the skylight, throw cable over the side, feed it in under the house and up into the living room, then they'd just have to attach the dish to the chimney, cut the cable from the reel and attach to the LNB, and fix the cable to the drainpipe.
Overall this would seem to be a minimal amount of work for the installers so probably something they'd be happy to do.
Does anyone else have experience of this and if so which cable would they recommend? From what I've read it sounds like the WF100 foam-filled 'shotgun' cable seems to be the one to go for & TLC seemed to have a reasonable price for it:
Twin Satellite Cable Foam Filled - Black
Thanks
Edit - on closer inspection, it looks like the TLC cable may be slightly thinner than this one -
http://www.satcure.co.uk/accs/page8.htm#WF100twin (I see they do cut lengths up to 20m). Does it look like a better quality option?