I have a number of white interior doors in my home which have a shiny surface, and appear to me to have a plastic coating.  I do not know if they are laminated or not.  They were fitted when my house was built about 5 years ago.  They now need some attention, but I have been advised not to paint them on account of the coating on them.  Any advice as to whether this is true or not, and if so, is there some other means of cleaning them?

Those doors are probably made of some modern laminate or other which are generally fairly easy to clean etc. You could try cleaning them with some Sugar Soap liquid and warm water and see if that works.  It usually works well.  Don't use harsh chemicals or you could do irreversible damage.


The advice you received regarding not being able to paint them is quite out of date - you can.  You can paint them with no trouble at all.  All you need is some ESP (available in most hardware, DIY and paint outlets) and some paint of your choice, probably an oil based satin or gloss depending on whether you would like them very shiny or not so shiny. 


If you plan to apply a new white coat you won't need an undercoat, however, if you plan to apply a very different colour to what is there already, you will need an undercoat to bridge 'the colour gap' To do the job, get a clean, lint free cloth and wipe the ESP on carefully taking care not to miss any spots. 


Leave it for about ten minutes and then wipe the excess film off gently with another similar cloth taking care to rotate the cloth regularly as this is a cleaning process also.  (don't be too vigorous as you don't want to remove the ESP film altogether) After about ninety minutes or more at normal room temperature, you can apply the paint directly.  Note, if, when you start painting, the paint starts to run away from the brush or 'crawls' as it is known, you will need to re-ESP that area because it will not have been done correctly. 


Depending on your finish etc, you could apply a second coat of the same paint, especially if using gloss, but you'll probably get a nice job done even with the one coat.  Actually here's a useful tip.  If you add about 10% or thereabouts of an additive like Owatrol oil to your paint, it will help the adhesion, hiding and coverage, leaving a beautiful brushmark-free finish.  You should be able to pick that up also in most of the better paint outlets.