Indoors? Outdoors? Ignore them outdoors, hoover them up (using the "crevice tool") when they're not on the compost indoors. Hoovering is surprisingly good for dealing with plagues of fruit flies / compost flies. Could you have been overwatering the "lovley plant"?

They may just like the smell...

Fungus gnats again! you guys must be having a plague of them over there!

Not that I've noticed.

I think they're very localised. We had a plague of them when we moved into the house we're in now a couple of years ago. The house had been empty for about 6 months, we arrived, then so did all the tiny flies. I spent weeks hunting them with the hoover - quite fun in its way - and they haven't been back since.