Not easy and full of problems unless you have a witness to the 'bump' or forensic evidence from the areas of damage to prove contact.

Section 170 Road Traffic Act 1988 requires where damage is caused to another vehicle for that driver to exchange details with any person requiring same and if not done to be reported to Police within 24 hrs. Both vehicles damaged both drivers should report.

So the matter is reported what does Plod do? Sends S172 name driver to other vehicles owner and then interviews. Firsly a very slight 'ding' in my opinion isn't going to go to Court for Due care, maybe fail to report but is the other drtiver going to admit. I doubt it. Independent/Forensic evidence required of contact. Further if the bump was slight was the other driver aware - if not then get out from fail to report charge.

Any CCTV in the area that may have caught the incident.?

Horrible as it may seem this is something for the Insurance to sort out or to protect no claims repair at own expense.

dvd

Where do I stand and what should I do? Thanks!

Where do you stand?

You have " a slight dent to the trim above my bumper " - You don't know how it was done or by whom. No witnesses. Police (rightly) won't be interested in trivial matters like this, it's not like a crime has been committed. So tough basically.

What should I do ?

Nothing, It's a min. 6 year old car with a "slight dent to the trim". Forget it

Even a forward-facing dash-cam fitted with sensors will register a bump outside of its field of vision, and put a time-stamp on it.