Have you done that before ? Does it actually get you anywhere ?
Yes and yes.
My wife and I have submitted over 500 instances of close passing, phone use, reckless overtakes since Nov 2018. 21 reports only were "no further action".
So, in Avon & Somerset reports do get acted upon, although we are only told that it is a "positive outcome" in that the driver will receive either a warning letter, a fixed penalty or a prosecution. Sometimes when a driver has contested the police's decision I have had to go to court, or provide a statement.
On a positive note, I regularly see drivers I've reported for close passes being more cautious around me.
These are Avon & Somerset's statistics for third party reporting from 12 months before Nov 2022.