if you dont want the seed as soon as the flowers finish. if you want seed then you have to wait for the pods to ripen and the seed ripe.

I cut mine down last weekend.

Basically, Lupins need to be cut back to the next leaf joint, as you might get another flower. When they've finished flowering for the year, as mine have, I cut the flowered stems right back to the base - unless you want to collect some seeds, of course.

You can also cut the dead stems off your Kniphofias (red hot pokers) as soon as you want to.

Thanks to both of you for helpful advice M