First Bad Experience Back in the UK

Let me start by saying that I love horses. They are gentle, amazing animals that give countless people endless pleasure. 
The two ladies in front of the car were doing their best to spoil it for all you horse-riders. 
I always slow up (to a crawl) when approaching or passing horses. To now, that has been acknowledged and appreciated by the riders. I did the usual today. They were ahead of us in a country lane. They had decided to ride side-by-side so that they could chat. OK, for a while. However, there was no recognition that we were behind, crawling along, waiting for them to find a point at which they could let us past. In fact, it was the opposite. They wanted to slow us. In the pic, you can see a car coming the other way. They screamed at it to reverse so that they could continue riding, side-by-side along the road.  They actually forced it backwards!  On a public highway, where cars pay a tax to use them. Oh, and there was a bridleway they could have been using, but had chosen not to. I do not know why. It was « rush hour » in the UK, when commuters return home, so they had a massive tail back in both directions. 
We slowed, to almost a stop as the riders were between the two cars. Then, one rider turned the horse round and started back towards us, telling us we were too close. In fact, she told us that we were a danger to her horses. She screamed at us. She was not pleasant at all. 
Eventually we got to a point where the road turned and they could move to one side to let others past - in both directions. (There had been other opportunities, but they had chosen to ignore them). 
More abuse followed as we passed them at last. 
I know they are not representative of the massive majority of horse riders, but they had chosen to make life as difficult as possible for car drivers at the busiest time of the commuting day. Why did they choose a narrow lane commuter route and not the bridleway nearby to have their ride at that particular time? I leave you to decide.