You don't want it! It's Himalayan Balsam - a major invasive pestilential weed. Also called "Noli Me Tangere" = Touch-Me-Not, as the seed capsules pop explosively. There's an article about how to control it here -http://www.dgsgardening.btinternet.co.uk/himalbals.htm

I think it might be friars balsam. It spreads like mad from its seed pods which "ping" and throw the seeds everywhere. You could live to regret it!

Posted at the same time Beattie!

I 'think' that this is Himalayan Balsam. If it is, it is a noxious weed and liable to be invasive. So many of our invasive palnts are very attractive, this is why they were intoduced in the first place.
All jumping in together on this one!

Three posts together again! :-) Are we quick off the mark, or what?

Having Google imaged your answer it seems you are all right!, It doesnt seem to have a great reputation, The majority of my garden is gravel with raised bedded areas, So I wonder if it may be possible to keep it under some kind of control as I quite like it and the height is perfect for the tropical area of my garden, Unless of course it will cause problems to other plants?? :?

I think you'll regret keeping it, as will your neighbours. It self seeds prolifically and fires hundreds of tiny seeds large distances. It grows very fast and smothers all other vegetation, being a particular problem when the seeds get into watercourses. I've been tempted to grow it too, but now accept that it's one of those plants that's just too aggressive to allow it to grow.

All right except that Impatiens noli-tangere is a different species to this one (and our only native member of the genus). The above is indeed Impatiens balsamifera from the Hiamalaya's.

So it is. The proper Impatiens noli tangere is yellow, and not as invasive I think. I should have checked, but the Himalayan Balsam is also called Indian Touch-Me-Not.

It is also a notifable weed and as such you are not allowed to let it grow on your land.

I have I. noli-tangere (well, really in parents garden) and they let it seed around in a slightly shaded border. As this one is native it's fine and the bees love it. It's easily removed too where not wanted. (see my photo's).

The other species as Owdboggy says is a different matter though!

To save trawling through my pics........

http://www.growsonyou.com/photo/slideshow/114938-touch-me-not/member/fractal

http://www.growsonyou.com/photo/slideshow/114936-touch-me-not/member/fractal