Usually traffic police take some time to attend. What you should do in such case - since it is clearly the fault of the one hitting ur car - provided that the other guy admits his/her fault, to report it to 999, get the phone number of the police station where you should go to finish paper work, call them, tell the story and give the details of both cars, get the name of the police officer getting the call or any reference number, then move there straight away after getting confirmation for that from the officer. I did that many times in similar cases.
Usually traffic police take some time to attend. What you should do in such case - since it is clearly the fault of the one hitting ur car - provided that the other guy admits his/her fault, to report it to 999, get the phone number of the police station where you should go to finish paper work, call them, tell the story and give the details of both cars, get the name of the police officer getting the call or any reference number, then move there straight away after getting confirmation for that from the officer. I did that many times in similar cases.