I can hear the argument with the CAA now;
Hmmm, since you can't quote actual references, you are quoting imaginery voices. Amusing, but no cigar.
"You can not legally do that unless you have an IR or IMC"
They wouldn't say this, because the "
that" is your claim about the legal prohibition on a VFR departure with IMC in the planned route. They might say "You can not legally fly in IMC unless you have an IR or IMC" but that is different from your claim.
Your imaginery conversation is just a restatement of your claim. It's completely circular. If I claimed heavier-than-air flight was illegal but couldn't find a reference, how would inserting the claim into an imaginery conversation help?
You also only construct examples where there is utter certainty that IMC conditions will prevail enroute or at the destination. A VFR flight departure in such circumstances is pointless, but not illegal. In reality of course, pilots are usually confronted with forecasts that suggest completing a VFR flight as intended is anything from "very likely" to "very unlikely" and everything in between. So more meaningful illustration would be
Pilot "I am departing VFR from A to B. The current forecast for B indicates that a VFR arrival will not be possible, but C and D nearby are forecasting VMC. There is also an enroute forecast that suggests I may have to turn back to A. I have enough fuel to maintain VMC and land safely in any of these outcomes, and I am willing to depart to see whether conditions turn out to be better than forecast."
DFC:"Stop, do not depart, that is illegal"
Pilot: "Where do you make this stuff up DFC? Of course it is legal"
I am not saying that the scenario I describe is good/bad, desirable or undesirable. I am saying that your claim that it is illegal to depart VFR in such a scenario is spurious.