Is this a salvia and is it a weed or worth keeping?

[fermi de Sousa]

This plant came up as a "volunteer" in my bulb bed and I don't recognise it at all! I can't remember getting the seed but it may've been dumped with some "frass" in the next bed and somehow got over to this bed. Otherwise it could just be a weed brought in by wildlife.
It won't be getting watered over the summer where it is, so if it's worth keeping I'll need to move it!
Any help would be appreciated,
cheers
fermi

[Lesley Cox]

If the leaves are greyish, it looks very like what we in NZ have as S. cyanescens tho' what is grown in the NH or at least by the lads from Bulgaria (where are they now?) is a much more compact and very desirable plant, woolly and violet-flowered. If yours has seed, keep it.

[Kees Jan]

Certainly looks like Salvia to me. No idea which species though. I think I would keep it  , looks worth growing and I don't think Salvia's have a reputation of becoming very invasive.