I tested the cable today and the IR reading was 3Mohms, which may pass now but probably wont for much longer, so I've told them its too dangerous to leave in, (don't wont a 3Mohms reading on a complete rewire).
But as a comprimise i've spent around 3 hours today getting the cables to the wall lights...I had to knife down the wallpaper via spirit level, peel back 0.5cm either side (very very carefully), scrape a very small channel for the cable to fit, fill the channel with filler. Tomorrow morning I'm to try to get the wallpaper to go back down with wallpaper repair paste. Hopefully it'll go back down ok, as these are the types of people who will withhold monies if they aint happy. If it turns out well i'll post a pic, if not, then I won't embarress myself further.