[rhyds]

I will say that in my experience VM are better regarding the technical standard of installs, as cable systems are interconnected and interference from one dodgy install could theoretically impact quite a few customers.

The basic problem is the piecework system the "installer" teams work under. As you mention the installers are required to do x amount of installs per day, and the system encourages corner cutting and rushing. I've heard of others being told by openreach installers that they could only have the master socket installed in a hallway (basically because the bloke didn't want the extra work of running some cable to where the customer actually wanted it)