I have never grown an olive so I am only going on common sense and gardening experience. Firstly I have seen small olives for sale, obviously intended as instant Mediterranean atmosphere rather than as long term features. So yours may be one of these ie it has been brought on as fast as possible to produce a pretty decorative plant rather than with a view to its future health. Secondly I think that your plant is unhappy indoors. It needs lots of sunshine, adequate water but good drainage and the wind in its hair to deter bugs and strengthen its roots. Yours may be sufferning from over/underwatering, dry air or temperature fluctuations, all of which can make plants drop their leaves. Unless it is in a big very bright atrium type place I would replace it with a tried and tested house plant and put your olive outdoors.

Thanks for the advice.

I have looked carefully at the plant today and feel I have an over watering problem.

The good news is that over the weekend several fresh new shoots & leaves have developed at the head of the plant.

I keep my fingers crossed and would still welcome any advice from anyone else who has grown this plant.