3) CHECK THE HIP YOURSELF - THOROUGHLY. One property we looked at seemed very nice. We looked carefully at the HIP when we had prised it out of the EA. The garage had been built over the main public sewer for the whole road - which was long, and old. The property developer who'd done that had then built an extension to give a fifth bedroom over the garage.
The HIP actually stated, "The map of waterworks does not indicate any water mains, resource mains or discharge pipes within the boundaries of the property.." The attached map showed the line of "contaminated water" going through the property boundary. Originally it had gone between the property and a detached garage, but the developer had moved the garage! So double-check looking at the maps. Incidentally a few HIP providers need to be sued as well.
This particular house dated back to the nineteenth century, so the sewers might be similarly dated. If there had been a serious problem then the water board might have had to pull down the garage and part of the house to repair the damage. If they'd needed 3m either side that would have involved demolition of the garage, the bedroom above it, a good chunk of the kitchen and part of the bathroom.
Now I don't think it would have gone that far - most of the manholes I've seen have not had a full 3m clearance each side. The one in our current (rented, built 2000) property is only 1m from the house. Still, I would not have wanted to run the risk of having part of the property *over* an old sewer run.
Would my solicitor have seen it? Probably not - he's a good solicitor, but not necessarily one who thinks its his job to scrutinise the maps, if the searches say, "no problem" in the text. The HIP regs mean that you have the ability to look at the maps yourself - do so.
BTW, I think HIPs regs do not apply to new houses, so that the OP could not have gone down that route. As I said, I'