I think if you decant your pot you might find the white maggots of vine weevil beetles eating at the roots. As the leaves are vanishing, other visitors, like the red lily beetle might also have paid a visit to your plant. Their maggots eat the leaves and turn into a red beetle rapidly, and produce more maggots to snack on your plant. Provera may be the answer. The best answer is, do like I do, and, admire other peoples Imperialis.

Frit imperialis are a big bulb that need lots of room to grow. I would not consider them as a pot plant and think that they would do better in the garden.
I don't hink that we yet have lily beetle anywhere in Scotland, yet, Dorjac, though I may be wrong. It has certainly not reached the northern half of the country but I would be interested to hear if it is in any other Scots gardens.

Thanks Bulbaholic I didn't realise Lily beetle hadn't got to Scotland.It's been in the south so long. I suppose there must be a climate barrier

"I suppose there must be a climate barrier"
It's known a cold, D! ;-).
I am still happy to be corrected on this, regarding the whole country.