Many moons ago, I was riding past a bus which was stopped in the bus lane on Lewisham High Street, just past the Ladywell Road junction; he was signalling to pull out but couldn't because of traffic, so I just went rather than hang about.
As I was about to reach the pinch point further up the road, where it goes under the railway bridge, said bus passed me and cut me up to the degree that I had to mount the pavement to avoid being hit.
He then stopped halfway up Molesworth Street; I pulled up and asked him what all that was about, and why did he try to do something so stupid; he refused to acknowledge me. As I was doing this, another cyclist told me he'd seen what had happened, and made sure the driver heard him say it.
We rode off together, discussing it, two abreast. It's a dual carriageway on that stretch. Next thing we know, the bus comes flying past us on the outside lane, honking his horn and trying to intimidate us. He then cut across us, and got stuck in the middle lane of three before the roundabout.
The other cyclist pointed at the bus's number plate, then at the driver, and told the driver he was going to report him, before heading up Loampit Vale. I picked my way through the traffic, and was waiting to go straight on, when the bus came past me, the driver calling me a "f**king w*nk*r", and pulled out onto the roundabout right in the path of traffic coming from the right; those drivers had to slam on hard to avoid t-boning the bus.
Now, I could take the cut-up, and the intimidation, and the abuse... But threatening the safety of his passengers and those other drivers was a step too far. So I wrote a letter to the bus company, outlining everything in detail, with the time, service number, reg. no., everything. I even said that it was such a shame, as I usually find bus drivers to be courteous and professional, and I was sorry that I felt I had to report this as it was so extreme.
The result? A letter, just like the OP's.
I honestly don't think I they give a flying one, so long as no-one gets killed or seriously injured.