We have the same problem where I live (a fairly remote village in the very North of Scotland). We wanted our windows replaced and upgraded to Triple Glazing, as it's extremely windy here even in summer. Found a firm in November (based about 80 miles away) who quoted said the work could be done around February as the windows are not standard sizes and would need to be made. The fitters finally arrived at the end of April, but the work is dreadful. I've sent letter after letter, email after email without response, and we are left with two windows that won't open at all (one of these arrived broken) and two more for which the ventilation is not complete. The bay window has gaps left between each angle (at windowsill level), and one of the coverings (between the angles) for the bay has already been blown off on a windy day because of the gaps at the base of the windows. Basically, straight windows have been fitted, each with straight sills, leaving the brickwork exposed at each angle.
I've now submitted a claim to the Small Claims Court (Sheriffs Court) to get back £5,000, which is the maximum that the Court can award (the total cost was over £12,000). Even if the original company come back now to do the required replacement windows and repairs, I would not trust them to do the work. I want to employ someone else, but who, how and when remains to be seen.
n.b. I've also written to "Rip Off Britain" and had no reply.