Is this a type of achillea?

It looks more like Tansy (Tanacetum vulgare) to me. It can be a thug, but as you say popular with the insect friends.

Thanx, Owdboggy. I always thought that Tansy flowers had many petals, a bit like dandelions. But the leaves on my plants are very similar, altho the flowerheads are petalless! Perhaps this is a "cultivated" or "gardenised" version?

It should have quite a distinctive smell not entirely pleasant. I too think it is Tansy and I think it has some medicinal properties, though i have forgotten what for !!!

Many, many thanx, folks, for your replies. following a sniff and google search, this is definitely TANSY. used for many ailments, notablly rheumatism, digestional ailments. I really do like this plant and always hope to have it, but beware, it will take over if you let it!