ANO Part 14 Operating Minima for Aerial Work And Private Aircraft:
109(2)(b) An aircraft operating for aerial work or privately shall not take off if the relevant RVR is less than 150m, unless in accordance with an approval from the country of registration.
I've edited the above part because I couldn't get it to cut and paste. The AAIB reports visibility in "tens of metres", Carl and Lee had a legal get out, They could have quoted Part 14 and if disciplined would have had the law on their side. Let alone no formal RVR reporting.
It comes back again to the fact that "Captaincy" isn't just pulling the levers and a thorough knowledge of the task you are on, you must have the facts available to protect yourself from the pressures you can come under.
SND