The state that the lillies are in would suggest that you are correct in that they have been forced for indoor pleasure. I would keep them indoors for now in a bright but cool room, if you have such a thing, and well watered. Enjoy them. When they have finished flowering it will probably be well into April and the worst of the winter will be well passed (I hope). Put the pots out into the garden and let the lillies die off naturally. It will help if you can give the occaisional feed with liquid tomato feed at this time. When the stalks have finally died, cut them off at the top of the pots, remove the bulbs and plant them in the garden or a planter, whichever you wish.

Thanks very much, Bulbaholic. That was what I thought should happen, nice to have it confirmed!
When will they flower again?

Late spring/summer next year Canalhopper.

Thank you!

I would do the same as Bulbaholic but I would cut the dead flowers off but leave the stem until it dies back.

Well, I've got two pots of lilies, so I could try one suggestion on each!
Thanks, Scotsgran.

The only reason for keeping the flowers would be so you could collect seed from the plants. I assume as they have already been forced there is no reason to stress the plant further. It sounds like a good experiment so if you do leave the flowers on one of them do remember to let us know if it made any difference. NB. the flowers grow out of the main stem and I only mean you to cut the flowers away - you need to allow the bulb to recover all it can from those green stems. They are a lovely colour. There looks to be three stems in each pot which probably means 3 bulbs, I would space the bulbs further apart, maybe 8" apart to give them the space to grow and spread.

Many thanks. I'll see how it all goes and report back.