Sacha wrote:

I think you're probably over-watering it and it doesn't need feeding until
late spring and then once a fortnight at most with perhaps, a seaweed
extract. Don't water it on any kind of strict regime, either now or in the
summer. Think of the conditions in which they grow naturally - cold winters
that can be wet, followed by blazing hot, very dry summers BUT, very
importantly, with sharp drainage on rocky land.
Wait until the pot is dry, not just looking a bit dry on top. Always let it
dry out between waterings and always make sure it's up on bricks or some of
those little clay feet, so that it can drain totally.
The type of compost is a mix of e.g. John Innes No. 3 and some multi-purpose
compost of a good quality.
I imagine your conservatory is frost-free? If it isn't your olive tree's
compost might be frozen and it can't take up moisture through its frozen
roots. This, too, will lead to severe leaf drop. Keep it in the sunniest
spot you can and make sure it's not frozen at night and only water it when
dry, letting it drain completely between waterings.

Thanks Sacha.

I have taken your advice on board. Not much will survive in a hot
conservatory, but olives will.