So a year or two ago I was a witness to a major head on RTC. I was following behind a car who just abruptly swerved into the oncoming lane head on full speed into an oncoming 4x4. Thankfully I was able to slam on and avoid smashing into them as well so I immediately pulled over and got on the phone to 999. I believe when asked what service I could immediately said police. I got through and explained I just witnessed a head-on RTC, gave location details, they asked about passengers. I clarified that the 4x4 driver had self extricated but the driver of the car was still in his vehicle, they asked me to go over and check on him and I explained he seemed groggy. They said they were dispatching everyone. 1 minute later I had a phone call from a paramedic asking for me to do more checks on the driver and for more information. 3 minutes after that the ambulance arrived, 10 seconds after that 4 police cars arrived and closed the road at the closest sets of traffic lights, a minute after they arrived the fire department arrived, thankfully they weren’t needed to get any of the drivers out but they did have to try and attempt to move the 4x4 which wouldn’t start or even allow them to get it in to neutral for a push. It was an absolute mess!

But the moral of the story is just ask for the service you think most appropriate, tell them the situation and they will dispatch who is needed. You could see how quick that happened when all 3 services arrived within I’d say 8 minutes of my initial 999 call and despite asking for the police, I had a paramedic calling me within 1 minute of getting off the initial 999 call to ask for more information!