Hi Dragon Green,
It sounds like you were stuck with one of the insurer windscreen co's as Brentacre don't have their own.
A couple of our main insurers do insist on using their own companies (or subsidiaries), and we're powerless to change that unfortunately, and generally this works really well. (Most insurers do the same TBH, it speeds up the claims process no end)
Not so long ago however, one of those insurers starting using a particular windscreen co, and I think they just got overwhelmed by the extra work. As weeks went on, problems were on the rise. We were on the phone daily chasing the companies up on behalf of our customers and shouting at the insurance company for letting them down. We do specialist vehicles, we don't want every Tom Dick and Harry company touching our windscreens, especially if they're going to mess it up! (I should add for balance that a large number were dealt with quickly and efficiently, not helpful for you, but for balance). After much work from our office manager and MD, we managed to encourage the insurer to back down and allow some third party companies to get involved on specific cases (classics etc), and eventually they gave in and moved everyone back to the system they had before which we knew and loved.
I apologise to anyone caught up in that, most went through, but when it went wrong... but rest assured we weren't sitting back watching everything fall apart, we were on every case individually pulling every string we could to push them through. At the end of the day, our customers pay our bills, not the insurers, so our loyalties lie with you first.
Apologies I'll stop short of replying to OP's request as we're not a forum sponsor and don't want to tread on toes.
Simon