I think it may depend on how far down the slug munched, but even if it ate a lot, this is early in the growing season in the UK and lupins very vigorous plants generally, so do not give up.
Sadly no guarantee that the slug or his friends will not eat any further lupin flowers : ((

Great, I love Lupins but the slugs & snails always get there first, little b's, so sadly I gave up on them.

I dont know if this will help you but I have wonderful, vibrant lupins in my front garden and they are never touched by snails or slugs.Which I have many of in my back garden. Also, the same plants have been coming back for 5 years now. What I found (By accident) that through a swimming pool deluge of bleached water onto my lupins (terrified that it would have killed them) it had the opposite effect. So now, every year I make sure I add a very small amount of bleach to a couple of the waterings and it has ensured my lupins viability. I am not sure why this is, and it does seem to go against what would be considered safe, but it works for me. Can anyone answer why this is?

Wish I could, Phleblady, but - no. I continue the fight against the slimies on my lupins, one of which has also had it's lovely flower spike eaten through, Great. But, look lower down and between the rosettes of new leaves and there will be the next compact flower bud. Lupins don't give up easy!

yes it will produce a new spike in time. I often chop spent spikes off and get a smaller one mid/late summer.

That's a strange thing about the bleach, I heard a tip once to put a small drop of bleach in the water for cut flowers to make them last longer but I've not been brave enough to try it.

The bleach sounds very interesting. In desperation I will have to try it. Nariz I have looked amonst the leaves ans can't see any more buds!!
weeding even my leaves have been muched . I always go out at night and kill all the slugs I see. So its not like im not trying. Slugs and snails I hate them. Granmage I know how you feel but I am trying not to let the little blitters win!!