Welcome to GOY. Where do you live, Martin? Does your olive stay outside all year round? It needs to be a VERY big pot for an olive to be happy, even here in Italy. We probably live a good way south of you, and even in the ground, in a really cold winter we get browning of leaves and even lose the trees altogether. May I suggest, if you don't have somewhere under cover (preferably light and not heated) to put the pot, if possible, you plant it out into the ground, and protect it with bubble wrap or even hessian during the cold months. You'll have to unwrap it occasionally for light and air on mild days. If not all the leaves are brown, cut off those that are, and hope that a little warm weather and sunshine will help it to recover. Please let us know how you get on.

Martin, has your olive tree been outside all winter? Where are you in the world? A photograph would be very helpful, but is the tree otherwise looking healthy, and is there any sign of new growth?

Thanks Gattina and Bamboo.It certainly looks like I need a larger pot.
The tree was in my conservatory all winter with no heat on.
I live in South Wales.I will re-pot and hope for the best.
Thanks.