Amelanchier is a great favourite . . . pretty white blossom in April, then pretty bronze leaves.

Golden Elderberry (Sambuccus aurea)

http://www.flickr.com/photos/31559373@N00/870003574/

Crataegus monogyna, the common hawthorn has an abundance of white flowers in early summer followed by red haws in the autumn. Good for bees and birds alike. Also a range of pink and scarlet, single and double flowers. Will do well on heavy clay soils.

Malus such as Paul's Scarlet or 'Gorgeous' get about that size, and produce crab apples in varying colours, depending on variety, in late summer and autumn.

I like all the above trees - all great ideas. To add, Prunus Kiki-shidare Zakura, an ornamental cherry is one to add as possibility.

As Jimmy says, the hawthorn is very hardy and supports a lot of wildlife. It is beautiful in both bloom and berry and grows to a lovely shape when it has room.
Personally I like the single blooms as they are better for the pollinating insects.
I have 2 white ones but would love a red or pink if only I had room!

I'd go for the Malus - lovely blossom and then the crab apples that you can use for jelly, wine or leave them for the birds.

Bamboo - Isn't 'Paul's Scarlet' a Crataegus, not Malus?

But for what it is worth, that would be my suggestion:-

Crataegus laevigata 'Paul's Scarlet'.

Thanks! Some good ideas. I already have 2 crab apples , which are lovely, 2 hawthorns, 2 sambuccas and a large ornamental cherry! It shows that eveyrone who commented knows exactly what would grow in my garden! I think I'll look out for an alemanchier so it's a bit different. If not then another hawthorn.

Yep Fractal cat, you're right - I meant Malus 'Profusion', thanks for the correction.

Went and bought an alemanchier yesterday afternoon ... and more besides! I can never go and buy 1 thing only :-) I now have a medlar tree too! Hope I can find a big enough space for it.

Good luck with them FlOss! I would like an amelanchier but would have to take something out in order to put it in! A medlar is something you don't see very often these days. I remember my mother telling me how she loved the fruit, which had to be really over ripe, apparently, but I've never tasted one myself.