There was no need for you to warn them, and you know that - you said yourself that they'd seen you; you did it because you were annoyed with them.Technically I was within my rights as the horn is an audible warning device. I did not initially use it as I said as I was not in a hurry but I assumed they would move over and the didn’t. In other words it was deliberate provocation. What got me was the deliberate non compliance with road markings to inconvenience me. Then as usual the moronic gestures because I’d had the temerity to warn them of my presence. No their behaviour is not defensible.
They were riding in an annoying fashion it sounds - I get that. However you had no need to 'horn them' as you put it.