Toothed Leaf 4 Toto :)

Sorry to take so long to reply Jacque. I have been looking through a few books to try and make sure. It looks very much like it could be. The name, apart from Sweet Rocket is Dames Violet or Hesperis matronalis. Below, I've printed what one of the books says.
Hesperis matronalis: Dames Violet. Stems 2 - 3ft. Stems 2 - 4 inches, broadly lanceolate; flowers white or lilac. Alien in plantations on wasteground, by waysides, river banks etc. Flowers May - July.
Another book says that the flowers are highly scented and that they are best grown as a biennial as they are fairly short lived. Apparently they grow easily from seed.
If this is what you have then sounds like a wonderful addition to your garden.
I know that Funkyfuschia thought that this was what it was all along so apologies to him for having doubts.