In Australia, and I am sure it will be the same in UK,
Instrument Flight TimeAll flight time during which the aircraft was controlled solely by reference to instruments may be recorded in the instrument 'Flight' column:
a) Time above overcast or at night in Visual Meteorological Conditions (VMC) is not counted as instrument flight;
b) In actual or simulated instrument conditions, only the pilot manipulating the controls or providing input to the auto-pilot may log all flight time as instrument flight;
c) A flight conducted on an Instrument Flight Rules (IFR) flight plan is not to be counted as instrument flight unless flying in IMC;
d) Instrument approaches are to be credited to the pilot (pilots, in the case of an airborne radar approach) manipulating the controls or providing input to the auto-pilot during the approach.
That is only 1 pilot can log instrument time (and the approaches) and during training that will be the student.
Interested to hear other views.
Paul