I had a similar incident a while ago:
I'm driving on an A road and look in my rear view mirror to see an Ambulance approaching quickly (lights on & siren on/off periodically), so I indicate left & pull up on the verge.
The car behind me then slows, blasts their horn at me and gives me a stinking look while pulling out around my car almost forcing the approaching Ambulance into on coming traffic. I think the driver thought I was just pulling over in a stupid place to use my phone or something but how can you miss a bl**dy big Ambulance with blues & twos on?!
Lot's of idiots on the road so you definitely have to keep your wits about you all the time.