Just to be clear Sharonchristine, has the 'incident' been reported to your insurer? If not, it's vital you do, as others have said. You say you have an engineer's report - is this from your own insurer - in which case all well and good? If you are innocent, it'd take some balls from the witnesses to swear on oath what they saw.
Couple of other points, it's only a hit-and-run/failure to report if you did it. But they've still got to prove it.
And, as an aside, the police don't have to get involved in personal injury cases if the incident has been reported to someone having reasonable grounds for wanting the details.