"I understand your point to be that it is illegal to depart on a VFR flight from A to B unless VMC is forecast for the entire flight."
No.
I said that it is illegal (and stupid) to depart on a VFR flight from A to B when you have determined by reference to a combination of actual and forecast weather information available to you that IMC conditions will or are likely to exist along the planned route.
The Rules of the Air are your reference for that.
The important issue is that you have to determine (you are pilot in command after all) what to do based on both actual and forecast conditions. Thus your argument about forecasts being not accurate enough falls down because you have tyo check actual conditions also.
The Rules of the air are quite specific in that they do permit you to depart (to have a look see) if you can not obtain the weather information pre-flight.
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When reading commnets about the accuracy of forecasts, I wonder if you are being confused by the idea of who determines if IMC exists. It is the PIC that makes the determination. It is not the met-office forecaster - they simply provide the information. The PIC uses the information available to decide. Forecasts these days rarely fall outside the prescribed limits of accuracy and when they do they are amended.
Are you guys saying that you can't make that decision? or are you saying that you are go minded despite the information showing that this is not a good plan and you sometimes get lucky and other times have to turn back but you will always go anyway and only turn back when you have to?
What did they teach you during PPL training?
Would an instructor ever let a student off on a crosscountry if they determined that IMC existed on the route? Would the instructor say - ah just take an extra hour's fuel and have a look and see?
The problem I have with this is that you see nothing wrong with what was done on the flight from Exeter to Blackpool right up until the point where the flight went IMC. You say that it is OK to depart Exeter on a flight planned in accordance with the requirements for a VFR flight but to a destination that is IMC and is forecast to remain so.
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IFR pilots kept killing themselves or nearly so by having a "look see" on approaches when the weather was well below limits. Then we had the approach ban - that will stop them from pushing the limits..........but it didn't so we have the approach ban and the absolute minima system to catch those that ignore the approach ban.
To me this simply says that many pilots will never learn.
Regards,
DFC