More likely an extremely heavy and untreated infestation of lupin aphid, a north American invader, which look greyish/white, usually first noticed on the stems, though they will have been under the leaves initially. They remain on the host plant all year, so treatment is necessary, if your lupin has survived the onslaught - use a systemic insecticide spray that treats for aphids, preferably in the evening when pollinating insects aren't working, but don't spray any open flowers nearby, and not on a windy day.

Thank you. The lupin which is affected is on its own, some distance from the others, so I'll dig it I up and get rid of it.

Check your other lupins though, particularly under the leaves,and keep an eye on them next year - these are flying insects and easily spread.

Looking at the photo I'm wondering if a lot of what is there is just dead or discarded skins. Before you do anything drastic I'd recommend that you give the area a firm blast of water preferably with a few drops of washing up liquid in the mix. Then reassess the damage