It's Figwort, Scrophularia nodosa. Apart from the smell, another distinguishing feature is its knobbly tuberous root, which grows mostly out of the ground. I think it's rather handsome, but I don't let it set seed.
Many thanks Felix! Any ideas where it might have come from? I have never seen it before (in any garden of mine), and it's not generally around here - how do the seeds spread?
By scattering. It's unusual to see colonies of Figwort, just the occasional striking individual. And where they originate is a mystery to me, too. If birds spread them, that would make more sense, but they don't.
We have fitgwort plants in our wild garden which come up in different places every year and the interesting thing we have found that the only insects attracted to the plants' insignificant flowers are wasps, never honey bees, bumblebees or any other insects!
I'm not sure where the seeds would have scattered from?
None of the gardens around us (our garden is up the side of a hill, there are gardens above and below) or to the side have it, and above the gardens is fields. It is all over our garden, in pots as well as in the ground, not just the odd plant, so I an mystified!
We do feed the birds - there is a very healthy crop of niger seedlings under it. Are Figwort seeds used in bird seed mix? That would make sense, except none of the plants are near the feeder, and some are up at the top of the garden, much higher than the feeder is.