Hmm.
Generally when I fly this way I will plan the route so that I have at least one section in CAS so the plan is entered into CFMU. I find doing this means I get hand offs into and out of the airways system and experience has shown that if you have been in the airways even for a fairly short way then things go smoothly.
Although to be fair I try to do all of my flying in the airways even short trips especially passing around London. You can't bust airspace when you are under positive control!!!!
So as I said, claiming to be IFR in VMC in order to get a better service is in my humble opinion reprehensible. While the controller is busy giving our friend a full radar service, the service to others asking for a FIS and a zone crossing is reduced needlessly.
So, let me get this straight...
Filing part of your route in airways so that you can benefit from the services of London Control to do all your coordination and planning while you cruise in VMC in class A, that's fine? The folks in TC have hardly anything to do anyway and so you might as well force them to soak up a bit of their workload crossing the TMA at 120 kt in your Cessna.
However, IFR in VMC outside controlled airspace to allow a controller, workload permitting, to offer a better service and coordinate you as an IFR flight, that's "reprehensible".
Was that the gist of it?