PaulF....the horsebox I mentioned was not a trailer being towed. It was an old box van type and was not getting up to any speed, even on straights. The road had limited straights for overtaking anyway and oncoming traffic combined with frustrated drivers caused some near misses. It was the driver’s attitude and inconsiderate behaviour in not pulling off the road that was the problem. She was quite indignant when spoken to so a simple chat was leapfrogged to a FPN. She was held at the lay by until traffic cleared but denied causing any problem. She drove out of the area but we guessed she would not change her driving.
There's no excuse. And if she had a nervous horse that traveled badly, all she had to do was to pull over when she saw a queue building behind her. After all, revving engines and dodgy overtakes will unsettle her horse.
In the days when we ran a lorry for the horses, our old Bedford TL would cruise at 50 - which should be ample to prevent a major build up of traffic. The Renault Midliner we had next would easily exceed its speed limit if you were not careful.