Having worked for a number of years in a role in Government where it was from time to time necessary to field such complaints from the public, this is known as the "polite p*ss off" letter. In other words sound reasonable, say nothing, give nothing away.
However, create enough public stink that my political masters think they may lose a few votes at election and that may be a different matter. Unfortunately for the latter, the reality is that anti terrorism is a vote winner. Photographers' rights is not. Besides public servants LOVE anti terrorism laws - more powers to them!
Many better commentators than I have written about the ,,,,(I was going to say slow but its actually been rapid) diminution of our rights as citizens in the holy name of anti terrorism. Governments of all pursuasions play this game. Most times in democracies they are benign. Sometimes they not. But the end result is loss of legitimate rights. Was there not a quote from George Orwell's Animal Farm or some such, about moving from a situation where all things not expressly forbidden are permissable ( in a democracy)o a situation (in a dictatorship) where all things not expressly allowed are forbidden.