Try get the witness to give you a witness statement and anyone else there that you recall being present, don't get a lawyer now you will be afforded the right to have one present in your interview and will be free for each interview you have to attend. I would call BTP and request that they recover any CCTV in or about the area, the cctv does not have to cover the area of the incident if its not there but show the manner in which the car was being driven, if this is not done you can bring it up in the interview, when you call always get the Officers name and collar number. (Council CCTV sometimes gets over written every 30 days)
I'm not a leagal advisor but i think your best course of action would to prepare a full statement, read that out on tape then go no comment to all other questions unless they will help in your defence. Also make sure you quote the crime ref number you were given for the incident you reported.
Not a nice situation to be in, but they have a duty to interview you either guilty or not.