What if the alleged offender performs the not uncommon act of burying the head in the sand and hoping it'll go away?
In my experience the report is investigated thoroughly before any Summons is issued, whether or not the alleged offender responds to their letter.
This is always necessary to protect a TOC from the adverse publicity that might arise from any reports that really shouldn't be pursued.
The reality is that despite the oft repeated comments on various forums about "incorrect" or "bad" prosecutions being brought by TOCs, there is virtually no evidence that this is the case.
Yes, very occasionally an alleged offender summonsed to Court may be acquitted, but that's the case in every sphere of criminal prosecutions.
Just ask yourself how many cases go through the Courts every week and are successful and then ask again, how many convictions result in an appeal and how many of those appeals succeed, then break that figure down again to determine how many are considered malicious prosecutions.
The fact is that it is so rare that the risk of such a case is incredibly small.
If an alleged offender "buries their head in the sand, hoping it will go away" as you put it, it is likely that they will be convicted in absence if indeed a summons is issued.
If a 'questionable' case were summonsed and if that case got to Court and a conviction was recorded in absence, it has to be recognised that in these circumstances, the conviction would be as a result of the defendant's contributory negligence in ignoring things.
If 'truly questionable evidence' were challenged at an early stage, I'm sure the case would never proceed to Summons