Cant see anyone in the car that they hit coming to too much harm.
other than emotional harm from having killed someone with your car you mean? Not to mention damage to their car that may well not be covered by insurance, nor for that matter the cost to society from dealing with accidents, closed roads, police investigations, medical services. No you are right no real risk of harm… Well unless there are any cyclist or motorcyclist coming up and meeting them head on?
Seems fairly obvious s28/29 RTA breach by anyone who crosses the carriageway, skids or crashes. And probably s31 for all the participants and the organiser.
It does look fun, like soap box / cartie racing (which can also be dangerous) but that is performed on closed roads, with marshalls etc. I’d say doing it on a live public road has the potential for a manslaughter charge.