Nigel,
I have flown in the UK and am familiar with the situation there.
I also qualified my views after the initial post so there was (or should have been) no confusion I based my comment upon the way we operate in the USA.
Our Rules are different than the UK which I also pointed out by referencing the FAR's, AIM, and TERPS.
The original Maintain VMC and a height sufficient to clear all obstacles (here it is within four miles of Track) and contact ATC Post is based upon the fact that we have very little Uncontrolled Airspace during IFR Operations resulting from IMC Weather being present.
Yes, the UK and USA are very different in the application of Controlled and Un-Controlled Airspace thus it is not an Apples to Apples comparison.
However, the decision making process is the same no matter where you operate.
If you elect to use a takeoff profile that requires Visual Reference until a specified set of Minima (IAS and Height Above Ground) then my insistence upon maintaining VMC applies. One aspect is a requirement for a Minimum Airspeed before engaging the AutoPilot System to fly the machine which is a consideration for the 139 unless I am mistaken.
If as some suggest the Take Off is done without using Outside References then there is no need for VMC to be maintained but you would still have to maintain clearance from all obstacles in your Take Off Path. How one does a "Vertical Take Off without Visual References" and still comply with the few Rules imposed upon you by the Authority is the trick to be accomplished.
How does one do that in the UK in a AW-139?