Thanks for your response.
The freezer is about three years old and was purchased as a non frost item.
I would say say that the ice formation on the back of the freezer is more of a thin film rather than heavy, however, with the freezer switched off it took some time to remove it with the application of warm cloths.
The major problem was what appeared to be a thicker icing behind the back plate. It was this that drew attention to the fault since one drawer would not return to position because of the pressure against the edge of the back piece. This stopped the door from closing.Leaving that shelf out allowed the door to close.
However, after having the unit defrosting for near 24 hours,when a good deal of water was produced, the shelf now fits into position and the door closes.
Have just switched the unit back on today, intending to ke p a close watch on what happens. There has to be some reason why the ice collection occurred in the first place.
I will keep you informed if there are any further developments.