Dave has asked me to expand on my post so,
We asked our Internorm reseller (EcoMerchant) to fit the glazing as we thought they would have an awareness of airtightness issues greater than that of a local glazing contractor. It turned out that they sub their fitting to a 3rd part firm, architect and builder had meetings with the the supplier and fitter to ensure that a fitting methodology was agreed prior to on site arrival of the glazing.
The glazing turned up en masse and fitting commenced, the fitter just got on with it for a few days before the architect popped by to look at the job. The tape used was actually not adhering very well to the wall construction (OSB) resulting in layers and layers of the stuff, especially around corners, and plenty of sagging. After the first airtest we realised that this was quite a big deal so most of the windows were removed, openings retaped (with a different tape after visit from tape supplier) and then refitted. Far from satisfactory.
In retrospect I think the main contractor's own chippies or glazing contractor with a day's training from the suppliers of tape and glazing would have taken things steadier and (probably) asked more questions of the site manager and architect rather than just fit everything and leave.
This is based only on our own experience which involved a main contractor with a brilliant attitude to problem solving, a great architect (Jon Broome) and input from Alan Clarke too.