Hi, these are lily beetle, if you look underneath the leaves you will find little piles of what is excreta which the larvae actually live in, you need to get this stuff off ,
you will find little grubs inside, squash them by any method you choose, the beetles themselves are very crafty, when you go near them they drop off the plant, they,re black underneath and drop onto their backs so you can,t see them on the soil.
The best thing to do, as they overwinter in the soil, is to remove the bulbs and plant in fresh compost for next year.insecticides don,t seem to have much effect on them so the best way to get rid is by hand.
Up until a few years ago, they were only in the south of england, but now they,ve spread further north, I don,t know if they,ve reached scotland yet, no doubt someone will let me know. derekm

They could be lily beetles. Have a look for them online and see if they match what you've seen.
Control seems to consist of picking them off and stomping on them, and their larvae that look like bits of bird poo on the leaves. The beetles tend to fall onto the ground upside down if they feel any vibration. This makes them very hard to spot, so you could carefully spread an old sheet or something similar under the plants first to catch the beetles when they fall.

I knock the little blighters into a yogurt pot and then tip them out and stamp on them and I use wet kitchen paper to wipe off the slimy larvae. Ugh! Horrible things! I had mediocre results with the lilies this year but a friend down the road sprayed beetles and larvae periodically with washing up liquid and had a lovely display of lilies, so that might be worth a try.

Provado now makes a spray which treats for lily beetle.

Thanks for the info Bamboo, I gave up on lilies because Igot fed up trying to get rid of them, disgusting creatures!! derekm

Well funnily enough, having been troubled for 5 years with lily beetle out on the balcony, this year, not a one, and the lilies were fab. I'd forgotten they were in the pot because there's a large clematis in it, but up they popped and flowered magnificently this year. I've never used the Provado, no idea how effective it is, but its the only treatment out there.