I have just had the following reply from the police:
"Many thanks for your email notifying us of a non-stop road traffic collision.
Please note that it would have been appropriate to inform us by telephone at the time of the incident, as Officers would have conducted a breatherliser procedure with the driver in question and in this context a 999 call would be justified.
It is correct to have reported this occurrence to us and Officers will make contact with you during the day."