No.
If you hit another car, get name address number plate and phone number. Your insurance will find theirs.
If they don't stop, then it is a police issue.
"i thought you had by law to give details to each other"
Yes, you do. You also have 24 hours to report the accident to the police if you fail to stop. Failing to stop, and failing to report the accident are two separate issues.
The only other time you'd call the police is if after the accident, if a car is stranded, or if someone is hurt or drunk.