plant ID

Yes, it's an introduced plant from North America called Ragweed (Ambrosia artemisiifolia).

They are members of the daisy family but like grasses, have abandoned insect pollination in favour of wind pollination. The flowers will extend into a column with male flowers at the top and females lower down.

Interesting plant and quite attractive foliage too.

Copy and paste this link below into your browser:

http://wisplants.uwsp.edu/scripts/detail.asp?SpCode=AMBART

How do you tell the difference between this and Tanacetum vulgare, Fractal?

It just doesn't quite tick all the characteristic boxes for me.

The leaves/leaflets of this plant come to a distinct tapered point and the branching habit is just wrong for Tansy. Tansy has a more ascending upswept branching habit plus Tansy doesn't look a regimented and tidy as this.

Have a look at the link I posted above. It's identical.

I have photos of the ordinary Tansy in my pics....similar to this but the growth habit is different...this one makes a nice balanced plant whereas the Tansy with pretty tiny yellow daisy type flowers sends runners underneath the surface of the soil...a bit of a thug really.

Plus, Ragweed (not to be confused with Ragwort) is an annual so you will either have to let it seed or collect the seed and re-sow.

Can I be very cheeky and if it does produce seed (lover half of the flower spike), could I have some please? :-)

No problem Fractal :o)
I'll collect some at the end of the season