How many fruit trees?

What is at the base of your raised bed - does it give access to soil?

This is not answer to your question, but just a few points...

I don't normally think of growing fruit trees in a raised bed. The idea about a raised bed is that it helps you to keep the soil open and well cultivated and provides good drainage. You don't normally cultivate the soil beneath a tree. Growing a tree on a raised bed might provide slightly better drainage, if you are on very poorly drained soil, but hopefully the roots will go deeper than that.

Presumably the trees will be fairly close together, in accordance with the suppliers instructions, and recommended planting distance. How close will depend on how vigourous the root stock is, and how big the trees are expected to grow. Much of the soil beneath them will be in shade, and you might not be able to cultivate it well for fear of damaging the roots of the trees. So what you can grow there, and well it grows, may be limited.

But I'm sure that some people do grow produce beneath trees, and they will be able to give you a better answer and some specific suggestions.

As regards what kind of fruit, then the answer really is - what do you like. You mention damsons, but I don't like them. You need to grow something that you will look forward to eating. Some people with a sweet tooth particularly like plums, or certain varieties of apple. I like cox, much more than other varieites, but it's a matter of personal taste.

You may need to be aware that many varieties of apple (and possibly other fruits) may require pollinators - other trees that will flower at the same time. The instructions about what you need are usually on tree labels, or in catalogues, or on the web.

Yes, you're right. You'd need a reasonable depth of soil. You say you've got 40cm. That would be more than a pot-grown plant would have.

And the trees won't cast much shade directly below, so you could grow something along the front.

For a cordon you need something to train the tree against, either a wall or wires. That tree is free standing. So it's a lot simpler.

I'd be surprised if you get anything like as much fruit as is shown in the illustration. It would be very interesting to know if anyone else has such trees, and how well they do crop.

Three trees - an apple, pear, and plum is certainly an interesting novelty package. For £50 you could buy a lot of fruit from a supermarket.

If you only have a limited amout of space, are fruit trees the best way of using that space. These trees do seem like a novelty, but that doesn't mean they are not interesting to grow, for the fun of it.

Some people might say that with a raised bed of that size you could grow 'vegetables to harvest all the year round'. That would involve a lot more work, but possibly be more interesting, and more useful. That would still be a 'fun thing', but of a different kind. You seemed to want to grow something beneath the trees. One option would be to forget the trees, and devote the bed wholly to vegetables.

There are other factors too, beyond our control. This year has been a poor year for fruit generally, and some people with large trees have ended up with virtually nothing.

I'm sure that many other people do grow fruit in a limited space. What are their views?