in the short term you wont die from it, so if it costs them time and hassle after the event so be it, hell mend them, no respectable installer would do such an install so you will prob find they are a cowboy, prob difficult to know when it is going in, but if you could be there and talk to the installer telling him you have contacted the variuos parties nd they are VERY interested to know who would do such an install you might spook them into walking, and if not tell them you will sue them for tresspass and damage to your property and also it would be nice to be sitting on your patio while they were working to see if they advise you of the hole coming through, imagine getting hit by some debris and getting injured, but wind them up by taking pics of everything they do, and their van and registration number etc, tell the neighbour she is wrong to instruct such work and will be left with a bill for £100's when it all goes belly up and her cowboy trots off into the sunset and she needs to get someone else in to fit it, and without saying anything at all to her it would be a great pity if her new flue kept getting blocked and shutting her boiler off