@Goldmember - Re: I used to be with BT...
This goes back to the early days of opening the network... Anyone remember Mercury Communications?
Anyway, Mercury used to lease lines from BT on a massive scale. The problem for BT was that if they even looked like they were giving preference to their own faults, as opposed to ones on Mercury lines, all hell broke lose with the regulators. So when a Mercury line developed a fault it was all hands to the pumps.
I believe this is still the case today, if not worse as the local loop is now opened up.
I'm sure that if Sky/TalkTalk et al get the slightest feeling of second class treatment, they're straight to the big red phone and contacting the regulator.
The result is as a BT customer, your engineer is likely to be pulled off your job (before he arrives) and sent to deal with a Sky customer.
Oh, and yes, I had a no-show for my Infinity install. No call, nothing. Eventually phoned them as 5pm to be told "Oh, he couldn't make it today".
At least that's better than what I see in the offices where I work... Engineers installing lines and cutting off other offices down the hall. Engineers turning up to setup broadband before the line is even live at the exchange... For a communications company they really suck at communication, even internally!