I realize it's been a long time since you asked your question and I hope you have already found an answer. Lilies are not the same as lilacs. Lilacs are a shrub and many lilies are bulbs. I don't know what a houseplant lily is in the UK, but I suspect it's an oriental or asiatic lily bulb. Did your plant look anything like this? Maybe it was fragrant?
If so, by now the foilage should have yellowed. You can plant the bulb in your garden in a sunny to part sunny location and it may return next year. Most bulbs that are forced for houseplants do not do well in succeeding years. If you can't plant it in the garden it's best to discard it.
Here's what a lilac looks like.
Thanks for your reply. Actually I have not found an answer yet. My flower is neither of those in the links. I think they are called baby calla lily but I am not sure. Anyway, they are in the shape of a funnel with a purple-ish colour. I think there will not be too many flowers with this funnel shape.
At the moment I just leave it in the pot in my home. I don't know if it will come back next year. Perhaps you could advise please?
You are so very welcome. Calla lilies are known botanically as Zantedeschia. Try and say that fast 3 times! I'm thinking you are in hardiness zone 8. That would mean you could plant your bulb in the ground and leave it there. They will even take a moist spot.
Here's several options for planting or keeping your bulb.