Laws and insurance policy terms can differ so you may not legally be required to notify your insurance company about an accident it is usually wise to do so. This way if the other party's insurance company denies the claim or you find out the other party was uninsured then your insurance company would have been informed of the accident and will be ready to help you place a claim through your collision coverage.

We would advise reporting any accident to your insurance company. Even minor ones, especially if there is a chance that you or the other party may place a claim.

Sometimes negligence laws allow both drivers to be found at fault, thus if both of you are found at fault then likely you would both are responsible for your own damages. So what you though at first may be a third party claim could turn into a first party claim.

It appears you are living in the UK. It is important to here as well to inform your own insurers of a potential car accident claim as soon as possible even though you may believe that it is not your fault.

The insurance company is likely to send out a Claim Form for you to complete and return to them. It is important to inform your insurers immediately because it is very often a term of the insurance policy that you do so; the penalty for not doing so could be your insurers refusing to indemnify you.