Scenario:-

2 agency workers pull up to park in our company car park before the start of their shift, they reverse as another car drives behind them. Very slow impact collision. Everybody gets out of their cars and have a big argument, then enter the building.
Both of the agency workers claimed they were injured. 1 went to hospital with whiplash the other went to the doctors with a limp. Neither of them returned to work.
Question:- if they don't return to work after 7 days do we need to fill in a RIDDOR report.

Not RIDDOR reportable as all were in motor vehicles let their insurance companies sort it out. Technically it is an RTC on private property.

With all due respect Road Traffic Crashes with regards to moving vehicles on public highways are not RIDDOR reportable. However using vehicles on private land e.g. a Landover ramming another Landover on a farmers lane/ councils play park / companies private car park does not necessarily fall under the definition of 'public highway' so in those cases RIDDOR then applies where the event happened when the people were at work

As to who should report then that is technically the employer but when using agencies this sort of thing should be sorted out at the contract stage noting that sometimes it is not practicable etc. for the agency (employer) to report as they are not there and have little/no control over their employee

And on the cynical side sometimes workers can get more £ from claims than they can do from working as rates of pay are so low in many industries

NB: I recently had a ten tonner go over spilling the load all over and spinning down an embankment coming to rest ~30m away from the lane - I could not get the police there as they said that the road was not a public highway so it was not their issue (they operate in an office only 40m away from me in a shared building)!

You need to make the decision about RIDDOR noting that the questions of 'were the people at work and did the event arise out of a work activity ' & 'does the Highways law cover our car park?' need evaluating noting that if your car park is very secure and is not an enticement etc. for the public then it probably does not come under highways law NB: pubs have private car parks but the can & do in many ways technically come under the Highways Act

With what U have said I would not report as the people were not at work nor did it arise out of a work activity even though the CP may be private land which does not come under highways law

Its not a RIDDOR as it is clearly an RTA - It was directly attributed to a road traffic accident (allegedly).

FYI - Whiplash can occur at any speed 5mph upwards and unless you have a black box it would be very difficult to substantiate the speed of the impact. Also, there was talk about a minimum mandatory, but this thought line was quashed as it will impact genuine cases.

I am guessing here, but it sounds like both vans are owned by your company. In which case I would be using your occupational health facility to substantiate or discredit these claims. Mentioning your concerns to the insurance company may initiate further investigation on their behalf.