Olives are fairly hardy Corise, having said that I lost mine in the big freeze of Dec. 2010, but of course that is the trees not the fruits. You have next to no chance of getting it to fruit in the UK but as an ornamental they are fine. As with most Mediterranean plants, the older, and bigger, it gets the hardier it will be but it will still require as sunny a spot as you can find for it. Soil, up to a pH of 8.5, is not very important and they are sparse feeders so no real problem. The only thing I would warn about is watching winter temperatures. If a severe frost is forecast then either drag it under shelter or get the fleece wrapped round it. I doubt if this current awful weather will affect it too much if it is already 8 ft tall.

I have 2 much smaller ones in pots and they survived this last winter very well, even with their branches weighed down with snow. The trick is to raise the pot off the floor and to wrap with fleece if you want to.
they prefer not to be without water so as long as the pot has good drainage then the wet weather shouldn't affect them.I also get flowers and small fruits on mine, but they havn't got much bigger because the cold weather makes them drop. I am surprised at how tough these plants are!!

I expected to lose ours in the dreadful winter we have just had (down to -22°c) and it did get quite a bit of leaf damage, but to our surprise, having chopped the damaged bits off, it is throwing out new shoots, and so are quite a few of our neighbours' trees. They are obviously much hardier than they are given credit for. I think extreme cold combined with prolonged damp in winter can be the killer. Ours had the advantage of being planted in the ground rather than a pot, so the roots were relatively well protected. If, however, you can haul the big pot to an unheated, but sheltered place of safety in winter, I think it would be wise. Sarraceniac is absolutely right about not needing to feed, and fleecing in bad weather, but make sure you "unfleece" it as soon as you possibly can, and don't use polythene as a protection - it doesn't insulate and it holds cold, damp air against the tree. We live in a Mediterranean country, but up a mountain, so not quite a typical Med climate, and we get flowers and mini-fruit, but they never get to maturity, either! I just love the trees for their amazing shape and colour. You can buy olives in jars!

I agree with Pam. I have a small potted Olive that is quite a few years old.....maybe ten. It has survived the last frosty winters. At the moment it is smothered in flowers. In the past it has grown small olives. Last winter it was not protected, as I was not able to fleece it up, as I broke my ankle. No harm done.