Solution

Three months and three days after the fitters failed to fit the bay window that had been manufactured the wrong size, despite smashing some of the surrounding brickwork, its replacement arrived. 

The bay is not symmetrical and its roof doesn't have the same profile as the brickwork below so fitting is a very skilled compromise. I have lost all faith in the windows firm and even though this crew were the much better fitters, who did the front door, I was very apprehensive. 

At one point a window firm director phoned me and said that the portable loo was in the way and needed to be moved. I told him that was a request that should have been made to the builders a fortnight ago, not to me on the morning of the fitting.

My builders' site manager, in whom I have total faith, was next door so ready to supervise and I took this photo at the stage at which I called him in when the fitter, then he, thought the replacement wasn't going to fit. 

I was very stressed and the site manager showed that not only is he a superb all-round builder but he also has excellent psychology skills: he took me into the kitchen and told me that if things went wrong they could be put right but that if I continued to stress I would come to hate my house and he couldn't put that right.

The fitters were here till almost 7pm and the site manager was going to stay until the end but once it became clear that the window would fit, and he'd showed me how the plasterboard would work inside, I told him he needed to get home. 

So now it is fitted, and the builders can come back in next week to finish the ceiling, do the plastering and connect electricity to the front of the house.