Black smoke isn't unburnt fuel it is due to poor and incomplete combustion of the derv in the combustion chamber due to many factors, basically incorrect fuel to air ratio,( excess fuel or insufficient air ) seen often on a turbo diesel when the pedal is floored and an initial puff of black smoke occurs momentarily till the turbo spools up and the correct fuel to air ratio is attained
White smoke on the other hand, not steam, is caused by raw fuel, i.e. unburnt fuel coming out of the exhaust, usually seen at first cold start on a worn engine or one where the heater plugs are u/s, again due to many causes, basically ignition temperature hasn't been reached in the combustion chambers and the atomised, unburnt fuel comes out of the exhaust with a prominent derv smell.
Blue hazy smoke obviously oil being burnt for various reasons.
Steam, obviously from water either in the fuel, coolant leak into combustion chambers, or especially with short journeys and a long time between journeys, as has been mentioned, a build up of water in the exhaust system which will need a good 20 or so miles fast run to get the full length of the system hot enough to boil the water off.
White and blue smoke and steam can look similar, a quick clue is that steam dissipates in the air quickly, blue smoke lingers with a smell of burning oil and white smoke lingers with a smell of derv.
When you say " The car has started to produce white smoke when ticking over and when under power."
On a hot engine white smoke from unburnt fuel wouldn't be expected to be seen and if fuel was not being burn't in a particular cylinder a consequent loss of power would be expected.
The causes of any of the above are many and varied so the first line of investigation is to determine if what you are seeing is from oil or water.
An exhaust gas test may show up some clues.
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