What about a lilac? I have grown "Katherine Havemeyer" (may be spelt incorrectly) and it is bushy with lovely double mauve flowers. You can shape and prune to bring more flowers. They are deciduous but the perfume is worth a few months of bare branches. Check them out as a bare rooted plant and they will be a bit cheaper. The colour range for lilacs is mauves, purple, pink and white, reddish, also purple/white ("sensation" I think it's called), so there's a reasonable selection of single and doubles. In the gardening books look up syringa as the alternative name.

Lilacs require a cold winter to flower well and perform much better in full sun. Beautiful flowers - I have several in different colours. All are old plants but nowhere near 4m high - and certainly much wider than 1m.

The dimensions you want are a bit of a problem. At 4m you want something that you don't want to be pruning to maintain the 1m width (unless you built a permanent scaffolding around it). The only thing that springs to mind is a conifer of some kind. But make sure it's going to stay within the 4m limit.

An Irish yew (Taxus baccata 'Fastigiata') might fit the bill. Ultimately, it would grow somewhat higher than 4m but not in your lifetime. It does eventually widen out at the top but, again, this is a feature of maturity.

What you would be looking at for at least the next ten to twenty years or so would be a very formal looking "punctuation mark". The leaves are very dark green and, unlike most conifers, are soft and feathery. The branches are very dense and upright. Small red berries are produced, rather than cones, and these tend to be hidden away in the foliage. Altogether, a highly desirable conifer.

There is a photo of a pair of yews on this site. Unfortunately, the photo doesn't really do the tree justice. You have to see one in real life to appreciate the beauty of the foliage.

There is also a golden variety but the few that I have seen growing tend to be quite yellow on the side exposed to the sun and green on the southern side.

The timber itself is very attractive and is highly desirable to wood-turners. And you could make your own longbow.

Here is a link that might be useful: http://www.hearstcastle.org/behind_scenes/plants/irish_yew.asp

Yew tree

A mock orange - murraya. Grow well in shade or sun. Hardy. beautiful fragrance when in flower. I've seen them in their natural state both growing tall and narrow, and tall and wide so I guess it depends on the conditions. Likes pruning though so easy to keep to the right size. Roots will fill up the area though, not invasive, just keen.
Some of the lilly pillys will grow to this shape in shade, and look really pretty.
Maybe a fruit tree like a weeping mulberry.
Or a rhododendron.