Arbutus unedo plainly ought to be very drought resistant given its natural habitat in mediterranean lands. Only this April I was walking through arbutus forests in Sardinia, where they have a very dry hot summer, though they grow only about 3m tall in such conditions. I saw taller ones in damper NW Portugal. Though I find mine is inclined to wilt in persistent dry conditions - perhaps you have to grow them hard to get them to be drought resistent.

Certainly the soils I have seen them growing on in the Med have mainly been thin acidic soils. But I'm pretty sure I've also seen them on limestone, in NE Sardinia, and I think the area in SW Ireland near Killarney where they are particularly abundant and tall, is limestone. Amazing that a plant should be so at home both in the cool, wet climate of SW Ireland and mediterranean areas with their hot dry summer.

I didn't recommend Arbutus, because they are inclined to become large trees in our climate. But I have a dwarf form in my garden. It said on the label it would only grow to 2m, but I have to prune it back hard every now and then, or it would soon be twice that size. It doesn't mind. Very tough tree/bush.

If I had the space to grow a full-size Arbutus, I'd choose Arbutus x andrachnoides. It has this amazingly showy shaggy red bark. Also more floriferous than my Arbutus, though my dwarf form is notedly less floriferous. It doesn't tend to fruit here though, as far as I can see. But it is a very big, vigorous tree. Some people near me have one, and they have to call in the tree surgeons about every 5 years to keep it from becoming enormous.

Someone mentioned Eucalptus. Many of those grow like a rocket and you can regret it as they are almost as ineradicable as ash. But there are smaller, more manageable Eucs, so if you do like them (like me) choose one of those. Relatively easily found smaller hardy Eucs include gregsoniana, pauciflora, nipophila, debeuzevillei. Among rarer small ones, I have E mannifera subsp mannifera and E nova-anglica, which are both in the very-rarely-seen-in-British-gardens category, and easier-to-find E pulverulenta which is more like a television aerial than a tree, though I'm coppicing it so it shouldn't do that, but will only be a small bush so treated. (My nova-anglica is not much different so far.)