Well, you're wrong again.
My quote comes direct from the CAA Safety Leaflet on the topic:
b) Radar Advisory Service (RAS):
This service is only available to flights operating
under IFR irrespective of meteorological
conditions and aims to provide you with the
information and the advisory avoiding action
necessary to maintain separation from other
aircraft. It is the radar service used by many
pilots, particularly when flying in IMC. But
remember, if you are:
• not qualified to fly in IMC, or
• qualified but out-of-practice,
you must NOT accept an advisory turn or
level change which will put you into IMC.
However, if you do not take the controller’s
advice, or if for any other reason you cannot
accept heading or level changes, you must
tell the controller, who may be able to offer
alternative avoiding action. You must also
inform the controller before making any other
changes in heading or level, because it may
affect your separation from other aircraft. If
you request RAS, but the controller is unable
to provide that service, you may be offered
RIS instead.
Flight under IFR only has to comply with certain rules; it does not prevent the Commander from making his own decisions where relevant.
The ATCO
cannot issue 'instructions' such as 'turn immediately' under a RAS. The fact that some do is being addressed in the revised ATSOCAS proposals.
You are correct in stating that a RAS cannot be offered to traffic flying under VFR - as no-one has denied.